Patterning process

ABSTRACT

A pattern is formed by coating a chemically amplified positive resist composition comprising a resin comprising acid labile group-containing recurring units and a photoacid generator onto a substrate, drying to form a resist film, exposing the resist film to high-energy radiation through a phase shift mask including a lattice-like first shifter and a second shifter arrayed on the first shifter and consisting of lines which are thicker than the line width of the first shifter, PEB, developing to form a positive pattern, illuminating or heating the positive pattern to eliminate acid labile groups for increasing alkaline solubility and to induce crosslinking for imparting solvent resistance, coating a reversal film, and dissolving away the positive pattern in an alkaline wet etchant to form a pattern by way of positive/negative reversal.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2009-030281 filed in Japan on Feb. 12, 2009,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a process for forming a pattern by way ofpositive/negative reversal involving the steps of exposure through alattice-like pattern mask including lines of different width anddevelopment to form a dense and isolated dot positive pattern,acid-generating and heating treatment for converting the positivepattern to be alkali-soluble and solvent-insoluble, coating thereon areversal film which is slightly alkali soluble, and effecting alkalinedevelopment to dissolve away a surface portion of the reversal film andthe positive pattern to form a negative pattern. More particularly, itrelates to a pattern forming process capable of simultaneously formingdense and isolated holes through a single exposure.

BACKGROUND ART

In the recent drive for higher integration and operating speeds in LSIdevices, the pattern rule is made drastically finer. Thephotolithography which is currently on widespread use in the art isapproaching the essential limit of resolution determined by thewavelength of a light source. As the light source used in thelithography for resist pattern formation, g-line (436 nm) or i-line (365nm) from a mercury lamp was widely used in 1980's. Reducing thewavelength of exposure light was believed effective as the means forfurther reducing the feature size. For the mass production process of 64MB dynamic random access memories (DRAM, processing feature size 0.25 μmor less) in 1990's and later ones, the exposure light source of i-line(365 nm) was replaced by a KrF excimer laser having a shorter wavelengthof 248 nm. However, for the fabrication of DRAM with a degree ofintegration of 256 MB and 1 GB or more requiring a finer patterningtechnology (processing feature size 0.2 μm or less), a shorterwavelength light source was required. Over a decade, photolithographyusing ArF excimer laser light (193 nm) has been under activeinvestigation. It was expected at the initial that the ArF lithographywould be applied to the fabrication of 180-nm node devices. However, theKrF excimer lithography survived to the mass-scale fabrication of 130-nmnode devices. So, the full application of ArF lithography started fromthe 90-nm node. The ArF lithography combined with a lens having anincreased numerical aperture (NA) of 0.9 is considered to comply with65-nm node devices. For the next 45-nm node devices which required anadvancement to reduce the wavelength of exposure light, the F₂lithography of 157 nm wavelength became a candidate. However, for thereasons that the projection lens uses a large amount of expensive CaF₂single crystal, the scanner thus becomes expensive, hard pellicles areintroduced due to the extremely low durability of soft pellicles, theoptical system must be accordingly altered, and the etch resistance ofresist is low; the postponement of F₂ lithography and the earlyintroduction of ArF immersion lithography were advocated (see Proc. SPIEVol. 4690, xxix, 2002).

In the ArF immersion lithography, the space between the projection lensand the wafer is filled with water. Since water has a refractive indexof 1.44 at 193 nm, pattern formation is possible even using a lenshaving a numerical aperture (NA) of 1.0 or greater. Theoretically, it ispossible to increase the NA to nearly 1.44. It was initially recognizedthat the resolution could be degraded and the focus be shifted by avariation of water's refractive index with a temperature change. Theproblem of refractive index variation could be solved by controlling thewater temperature within a tolerance of 1/100° C. while it wasrecognized that the impact of heat from the resist film upon lightexposure drew little concern. There was a likelihood that micro-bubblesin water could be transferred to the pattern. It was found that the riskof bubble generation is obviated by thorough deaeration of water and therisk of bubble generation from the resist film upon light exposure issubstantially nil. At the initial phase in 1980's of the immersionlithography, a method of immersing an overall stage in water wasproposed. Later proposed was a partial-fill method of using a waterfeed/drain nozzle for introducing water only between the projection lensand the wafer so as to comply with the operation of a high-speedscanner. In principle, the immersion technique using water enabled lensdesign to a NA of 1 or greater. In optical systems based on traditionalrefractive index materials, this leads to giant lenses, which woulddeform by their own weight. For the design of more compact lenses, acatadioptric system was proposed, accelerating the lens design to a NAof 1.0 or greater. A combination of a lens having NA of 1.2 or greaterwith strong resolution enhancement technology suggests a way to the45-nm node (see Proc. SPIE Vol. 5040, 724, 2003). Efforts have also beenmade to develop lenses of NA 1.35.

One candidate for the 32-nm node lithography is lithography usingextreme ultraviolet (EUV) radiation with wavelength 13.5 nm. The EUVlithography has many accumulative problems to be overcome, includingincreased laser output, increased sensitivity, increased resolution andminimized line-width roughness (LWR) of resist coating, defect-free MoSilaminate mask, reduced aberration of reflection mirror, and the like.

The water immersion lithography using a NA 1.35 lens achieves anultimate resolution of 40 to 38 nm as the half-pitch of a line patternat the maximum NA, but cannot reach 32 nm. Efforts have been made todevelop higher refractive index materials in order to further increaseNA. It is the minimum refractive index among projection lens, liquid,and resist film that determines the NA limit of lenses. In the case ofwater immersion, the refractive index of water is the lowest incomparison with the projection lens (refractive index 1.5 for syntheticquartz) and the resist film (refractive index 1.7 for prior artmethacrylate-based film). Thus the NA of projection lens is determinedby the refractive index of water. Recent efforts succeeded in developinga highly transparent liquid having a refractive index of 1.65. In thissituation, the refractive index of projection lens made of syntheticquartz is the lowest, suggesting a need to develop a projection lensmaterial with a higher refractive index. LuAG (lutetium aluminum garnetLu₃Al₅O₁₂) having a refractive index of at least 2 is the most promisingmaterial, but has the problems of birefringence and noticeableabsorption. Even if a projection lens material with a refractive indexof 1.8 or greater is developed, the liquid with a refractive index of1.65 limits the NA to 1.55 at most, failing in resolution of 32 nmdespite successful resolution of 35 nm. For resolution of 32 nm, aliquid with a refractive index of 1.8 or greater and resist andprotective films with a refractive index of 1.8 or greater arenecessary. Among the materials with a refractive index of 1.8 orgreater, the high refractive index liquid seems least available. Such aliquid material has not been discovered because a tradeoff betweenabsorption and refractive index is recognized in the art. In the case ofalkane compounds, bridged cyclic compounds are preferred to linear onesin order to increase the refractive index, but the cyclic compoundsundesirably have too high a viscosity to follow high-speed scanning onthe exposure tool stage. Since hafnium oxide particles have hightransparency and a refractive index in excess of 2 at 193 nm, it isunder study to form a high refractive index liquid by dispersing theparticles in water or alkane solvents. However, to increase therefractive index up to 1.8, hafnium oxide must be dispersed in water inan amount of at least 30 wt %. The resulting mixture has a very highviscosity which is incompatible with high-speed scanning. If a liquidwith a refractive index of 1.8 is developed, then the component havingthe lowest refractive index is the resist film, suggesting a need toincrease the refractive index of a resist film to 1.8 or higher.

The process that now draws attention under the above-discussedcircumstances is a double patterning process involving a first set ofexposure and development to form a first pattern and a second set ofexposure and development to form a pattern between the first patternfeatures. See Proc. SPIE Vol. 5754, 1508 (2005). A number of doublepatterning processes are proposed. One exemplary process involves afirst set of exposure and development to form a photoresist patternhaving lines and spaces at intervals of 1:3, processing the underlyinglayer of hard mask by dry etching, applying another layer of hard maskthereon, a second set of exposure and development of a photoresist filmto form a line pattern in the spaces of the first exposure, andprocessing the hard mask by dry etching, thereby forming aline-and-space pattern at a half pitch of the first pattern. Analternative process involves a first set of exposure and development toform a photoresist pattern having spaces and lines at intervals of 1:3,processing the underlying layer of hard mask by dry etching, applying aphotoresist layer thereon, a second set of exposure and development toform a second space pattern on the remaining hard mask portion, andprocessing the hard mask by dry etching. In either process, the hardmask is processed by two dry etchings.

While the former process requires two applications of hard mask, thelatter process uses only one layer of hard mask, but requires to form atrench pattern which is difficult to resolve as compared with the linepattern. The latter process includes the use of a negative resistmaterial in forming the trench pattern. This allows for use of highcontrast light as in the formation of lines as a positive pattern.However, since the negative resist material has a lower dissolutioncontrast than the positive resist material, a comparison of theformation of lines from the positive resist material with the formationof a trench pattern of the same size from the negative resist materialreveals that the resolution achieved with the negative resist materialis lower. After a wide trench pattern is formed from the positive resistmaterial by the latter process, there may be applied a thermal flowmethod of heating the substrate for shrinkage of the trench pattern, ora RELACS method of coating a water-soluble film on the trench pattern asdeveloped and heating to induce crosslinking at the resist film surfacefor achieving shrinkage of the trench pattern. These have the drawbacksthat the proximity bias is degraded and the process is furthercomplicated, leading to reduced throughputs.

Both the former and latter processes require two etchings for substrateprocessing, leaving the issues of a reduced throughput and deformationand misregistration of the pattern by two etchings.

One method that proceeds with a single etching is by using a negativeresist material in a first exposure and a positive resist material in asecond exposure. Another method is by using a positive resist materialin a first exposure and a negative resist material in a higher alcoholof 4 or more carbon atoms, in which the positive resist material is notdissolvable, in a second exposure. However, these methods using negativeresist materials with low resolution entail degradation of resolution.

A method which does not involve PEB and development between first andsecond exposures is the simplest method with high throughput. Thismethod involves first exposure, replacement by a mask having a shiftedpattern drawn, second exposure, PEB, development and dry etching.However, the optical energy of second exposure offsets the opticalenergy of first exposure so that the contrast becomes zero, leading to afailure of pattern formation. If an acid generator capable of two photonabsorption or a contrast enhancement layer (CEL) is used to providenonlinear acid generation, then the energy offset is relatively reducedeven when second exposure is performed at a half-pitch shifted position.Thus a pattern having a half pitch corresponding to the shift can beformed, though at a low contrast. See Jpn. J. Appl. Phy. Vol. 33 (1994)p 6874-6877, Part 1, No. 12B, December 1994.

The critical issue associated with double patterning is an overlayaccuracy between first and second patterns. Since the magnitude ofmisregistration is reflected by a variation of line size, an attempt toform 32-nm lines at an accuracy of 10%, for example, simply requires anoverlay accuracy within 3.2 nm. The advanced ArF immersion lithographyscanner has an overlay accuracy of the order of 8 to 6 nm for everywafer on a common exposure tool. The term “every wafer” means that theexposure tool carries out alignment relative to a resist alignmentpattern which has been formed by exposure and development. Herein asignificant improvement in accuracy is necessary. If first and secondexposures are carried out without demounting the wafer from the chuck,the positional shift associated with chuck remounting is cancelled andthe alignment accuracy is improved to the order of 5 to 4 nm. In thecase of double patterning, the process of carrying out plural exposureswithout demounting the wafer from the chuck becomes an exposure processwhich can be implemented on account of the improvement in alignmentaccuracy. In the exposure process intended to reduce the pitch to halfby utilizing a nonlinear energy distribution such as the two-photonabsorption resist, continuous exposure is carried out while shifting theexposure position by ¼ of the pitch and without demounting the waferfrom the chuck. The nonlinear resist or CEL which is sensitive toradiation of 193 nm wavelength has not been reported. If such a resistwere developed, the double exposure process with the minimum alignmenterror would become practical.

In addition to the double patterning technique, the technology forforming a fine space pattern or hole pattern includes use of negativeresist material, thermal flow, and RELACS as mentioned above. Thenegative resist material suffers from the problems that the resistmaterial itself has a low resolution and bridges form in a fine holepattern because the negative resist material relies on the crosslinkingsystem. The thermal flow and RELACS methods suffer from a likelihood ofvariation during dimensional shrinkage by heat.

FIG. 1 illustrates a process for forming a hole pattern using a positivephotoresist material. In FIG. 4A, a photoresist material is coated ontoa processable substrate 101 on a substrate 100 to form a photoresistfilm 102. In FIG. 4B, the photoresist film 102 is exposed to lightthrough a photomask having the desired pattern and developed to form aphotoresist pattern 102 a. In FIG. 4C, the processable substrate 101 isetched while using the photoresist pattern 102 a as a mask.

The method of forming a negative pattern by reversal of a positivepattern is well known from the past. For example, JP-A 2-154266 and JP-A6-27654 disclose naphthoquinone resists capable of pattern reversal.JP-A 64-7525 describes exposure of selected portions of a film tofocused ion beam (FIB) for curing and flood exposure whereby the curedportions are left behind. JP-A 1-191423 and JP-A 1-92741 describeexposure of a photosensitive agent of naphthoquinone diazide to form anindene carboxylic acid, heat treatment in the presence of a base into anindene which is alkali insoluble, and flood exposure to effectpositive/negative reversal. FIG. 2 illustrates this positive/negativereversal method. In FIG. 2A, a photoresist material is coated onto aprocessable substrate 101 on a substrate 100 to form a photoresist film102. In FIG. 2B, the photoresist film 102 is exposed to light through aphotomask having the desired pattern and heated. In FIG. 2C, thephotoresist film 102 is subjected to flood exposure. FIG. 2D illustratespattern reversal by development to form a reversed pattern film 103. InFIG. 2E, the processable substrate 101 is etched while using thereversed pattern film 103 as a mask.

As to the positive/negative reversal method including exchange ofdevelopers, attempts were made to form negative patterns by developmentin an organic solvent of hydroxystyrene partially protected withtert-butoxycarbonyl (t-BOC) groups, and by development withsuper-critical carbon dioxide.

As to the positive/negative reversal method utilizing silicon-containingmaterials, it is proposed to form a fine hole pattern by covering aspace portion of a positive resist pattern with a silicon-containingfilm, effecting oxygen gas etching for etching away the positive patternportion, thus achieving positive/negative reversal to leave asilicon-containing film pattern. See JP-A 2001-92154 and JP-A2005-43420. FIG. 3 illustrates this positive/negative reversal method.In FIG. 3A, a photoresist material is coated onto an underlayer film 104on a processable substrate 101 on a substrate 100 to form a photoresistfilm 102. In FIG. 3B, the photoresist film 102 is exposed to lightthrough a photomask having the desired pattern and developed to form aphotoresist pattern 102 a. In FIG. 3C, the photoresist pattern 102 a iscrosslinked. In FIG. 3D, a SOG film 105 is formed on the underlayer film104 and so as to cover the crosslinked photoresist pattern 102 a. FIG.3E illustrates light etching with CMP or CF gas until the crosslinkedphotoresist pattern 102 a is exposed. FIG. 3F illustrates patternreversal by oxygen or hydrogen gas etching. In FIG. 3G, the processablesubstrate 101 is etched while using the patterned SOG film 105 as amask.

As compared with the line pattern, the hole pattern is difficult toreduce the feature size. In order for the prior art method to form fineholes, an attempt is made to form fine holes by under-exposure of apositive resist film combined with a hole pattern mask, resulting in theexposure margin being extremely narrowed. It is then proposed to formholes of greater size, followed by thermal flow or RELACS method toshrink the holes as developed. However, there is a problem that controlaccuracy becomes lower as the pattern size after development and thesize after shrinkage are greater and the quantity of shrinkage isgreater. It is then proposed in Proc. SPIE, Vol. 5377, 255 (2004) that apattern of X direction lines is formed using a positive resist film anddipole illumination, the resist pattern is cured, another resistmaterial is coated thereon again, and a pattern of Y direction lines isformed in the other resist using dipole illumination, leaving a gridline pattern, spaces of which provide a hole pattern. Although a holepattern can be formed at a wide margin by combining X and Y lines andusing dipole illumination featuring a high contrast, it is difficult toetch vertically staged line patterns at a high dimensional accuracy. Itis proposed in IEEE IEDM Tech. Digest 61 (1996) to form a hole patternby exposure of a negative resist film through a Levenson phase shiftmask of X direction lines combined with a Levenson phase shift mask of Ydirection lines. Since the maximum resolution of ultrafine holes isdetermined by the bridge margin, the crosslinking negative resist filmhas the drawback that the threshold size is large as compared with thepositive resist film.

As compared with white spots, a pattern of black spots can be formed toa fine size. As the hole size is reduced using a highly transparenthalftone or chromeless phase shift mask, white spots are reversed intoblack spots, after which very small black spots with a high contrast areformed. It is reported in Proc. SPIE Vol. 4000, 266 (2000) to form densefine holes by combining this concept with a negative resist film. Acombination of a halftone phase shift mask having a high transmittanceof 20% with a negative resist film provides a mask error enhancementfactor (MEEF) of 0 (see Proc. SPIE Vol. 5040, 1258 (2003)).

When the super-resolution technology is applied to repeating densepatterns, the pattern density bias between dense and isolated patterns,known as proximity bias, becomes a problem. As the super-resolutiontechnology used becomes stronger, the resolution of a dense pattern ismore improved, but the proximity bias is exaggerated. In particular, anincrease of proximity bias in a hole pattern poses a serious problem.One common approach taken to suppress the proximity bias is by biasingthe size of a mask pattern. Since the proximity bias varies withproperties of a photoresist material, specifically dissolution contrastand acid diffusion, the proximity bias of a mask varies with the type ofphotoresist material. For a particular type of photoresist material, amask having a different proximity bias must be used. This adds to theburden of mask manufacturing. Then the pack and unpack (PAU) method isproposed in Proc. SPIE Vol. 5753, 171 (2005), which involves strongsuper-resolution illumination of a first positive resist to resolve adense hole pattern, coating on the first positive resist pattern anegative resist film material in alcohol solvent which does not dissolvethe first positive resist pattern, exposure and development of anunnecessary hole portion to close the corresponding holes, therebyforming both a dense pattern and an isolated pattern. One problem of thePAU method is misalignment between first and second exposures, as theauthors point out in the report. The hole pattern which is not closed bythe second development experiences two developments and thus undergoes asize change, which is another problem.

CITATION LIST

-   Patent Document 1: JP-A H02-154266-   Patent Document 2: JP-A H06-027654-   Patent Document 3: JP-A S64-7525-   Patent Document 4: JP-A H01-191423-   Patent Document 5: JP-A H01-092741-   Patent Document 6: JP-A 2001-092154-   Patent Document 7: JP-A 2005-043420-   Patent Document 8: JP-A 2007-171895-   Patent Document 9: JP-A 2006-293298-   Non-Patent Document 1: Proc. SPIE Vol. 4690, xxix (2002)-   Non-Patent Document 2: Proc. SPIE Vol. 5040, 724 (2003)-   Non-Patent Document 3: Proc. SPIE Vol. 5754, 1508 (2005)-   Non-Patent Document 4: Jpn. J. App. Phys. Vol. 33 (1994), 6874-6877,    Part 1, No. 12B, December 1994-   Non-Patent Document 5: Proc. SPIE Vol. 5377, 255 (2004)-   Non-Patent Document 6: IEEE IEDM Tech. Digest 61 (1996)-   Non-Patent Document 7: Proc. SPIE Vol. 4000, 266 (2000)-   Non-Patent Document 8: Proc. SPIE Vol. 5040, 1258 (2003)-   Non-Patent Document 9: Proc. SPIE Vol. 5753, 171 (2005)

DISCLOSURE OF THE INVENTION

When it is desired to form a very fine hole pattern, the double dipolelithography using a negative resist film and masks of X and Y directionline patterns suffers from the problems that the fine pattern cannot beformed due to low resolution as compared with a positive resist film,the throughput is reduced by two exposures involved, and a sizedifference arises between dense and isolated patterns. If a positivepattern once formed with a high resolution can be reversed into anegative pattern, the problems associated with the use of a negativeresist film are overcome. If the exposure process capable of achievingthrough a single exposure a high resolution equivalent to the doubledipole lithography is applicable, the problem of reduced throughput isovercome. The problem of a size difference between dense and isolatedpatterns is overcome by applying mask pattern correction or opticalproximity correction (OPC) with a proximity bias taken into account.

As discussed above, a variety of methods were reported for reversal intoa negative pattern of a positive image obtained from a positive resistfilm featuring a high resolution capability. In particular, theabove-cited JP-A 2005-43420 refers to an organic solvent-basedcomposition as the silicone-based burying material for positive/negativereversal. The previous method using a water-soluble silicon resin as thereversal film-forming material has the problem that if an organicsolvent-based reversal film-forming material composition is coated ontoa substrate having a positive pattern formed thereon, the positivepattern can be disrupted by the organic solvent used for coating. If theresist pattern-forming resin is insolubilized against organic solvent bycuring the resist resin with EB or the like to induce crosslinkingbetween molecules of the resist resin, then an organic solvent-basedreversal film-forming material composition may be utilized, enabling achoice from a wider range of materials. Where this treatment is done,however, the removal of the resist pattern at the final stage forreversal cannot resort to removal by dissolution because the positivepattern has been insolubilized. The state-of-the-art technology relieson no other means than removal by reactive dry etching. Then aselectively dry etchable material containing silicon, titanium or thelike must be selected as the reversal film-forming material. In oneprocess, a silicon resin coated on a resist pattern is etched back withan etching gas such as fluorocarbon gas to expose the surface of theresist pattern, after which dry etching with oxygen and hydrogen gasesis carried out for image reversal. For image reversal, two etching stepsincluding etching back and etching and concomitant gas exchange arenecessary. With this process, throughput is reduced.

On the other hand, JP-A 2001-92154 discloses advantageous removal of apositive pattern by wet etching. In the disclosed method, once apositive pattern is provided, an organic solvent solution of anorganosilicon compound is directly (without any special treatment)coated to form a reversal film of organosilicon. The patent does notrefer to the damage to the positive pattern by intermixing. The patentdescribes that for the preparation of an organosilicon composition, highpolarity solvents (e.g., hydroxyl-bearing compounds such as propyleneglycol monomethyl ether and lactic esters, esters such as PGMEA, andketones such as acetone) may be utilized as well as low polaritysolvents (e.g., toluene and cumene), although only toluene and cumeneare used in Examples. The inventors made a follow-up test by using asolvent containing a high polarity solvent such as PGMEA, ethyl lactate,propylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol monopropyl ether, propylene glycol monobutyl ether orcyclohexanone as the solvent for reversal film, and coating anorganosilicon solution in such a solvent onto a positive pattern whichhad been subjected to no particular treatment. Then the pattern becamedissolved in the coating solvent, and the test failed to achievepositive/negative reversal at the required accuracy level. It wasdemonstrated that this method can adopt only a reversal film-formingmaterial exhibiting a high solubility in low polarity solvents, but notreversal film-forming materials having a high concentration of polargroups featuring substrate adhesion, such as novolac resins,polyhydroxystyrene polymers, and alicyclic polymers having a highcontent of hydroxy groups or lactone.

When a negative resist material is used in the double dipole lithographyutilizing dense X direction lines and intersecting dense Y directionlines, a highly dense hole pattern approximately equivalent to themaximum resolution of lines is obtainable. The double dipolelithography, in the case of full-field exposure, requires two exposureswhile exchanging two masks. When it is desired to form a logic devicepattern where dense pattern regions are combined with isolated patternregions, two double dipole illumination exposures of dense pattern andone exposure of unnecessary pattern region are necessary, totaling tothree exposures. A significant loss of throughput is unavoidable.

The state-of-the-art exposure system has one mask stage and is notconstructed such that exposures are effected on a single wafer whileexchanging three masks. Alignment is necessary whenever the mask isexchanged. The process time includes the times of three exposures plusthe times of mask exchange and concomitant alignment, leading to asignificant loss of throughput.

An object of the invention, which is made to achieve an improvementunder the above-described circumstances, is to provide a process forforming a pattern including using a positive resist film, singleexposure to form both a dense dot pattern and an isolated dot pattern,and positive/negative reversal of the dot pattern into a hole pattern.

By baking at high temperature the substrate having the positive dotpattern formed thereon such that the pattern is endowed with minimalnecessary resistance to an organic solvent to be used in the reversalfilm-forming composition while it maintains a solubility in an alkalineetchant, there is provided a process for forming a hole pattern by wayof positive/negative reversal wherein the step of finally forming anegative image is carried out by wet etching with an alkaline etchant.Then not only silicon base materials, but also organic non-siliconeresins such as aromatic resins and polycyclic resins are applicable asthe reversal film-forming composition. In addition, hydroxy-bearingsolvents and highly polar solvents such as esters and ketones may beused as the solvent to formulate the reversal film-forming composition.There is provided a process for forming a pattern by way ofpositive/negative reversal that can form a hole pattern including bothdense holes and isolated holes with a wide margin.

The inventor has found that by exposing a positive resist through aphase shift mask including lattice-arrayed shifters having differentline size, a positive resist pattern consisting of dots only at theintersections between thick lines can be formed. That is, the inventorhas discovered an exposure method capable of forming both dense andisolated dot patterns through a single exposure. If the resin in thepositive resist pattern is subjected to partial crosslinking treatment,then crosslinking takes place to such an extent to provide necessaryorganic solvent resistance while maintaining a solubility in alkalinewet etchant. If the foregoing steps are incorporated in the negativepattern forming process relying on positive/negative reversal, then notonly conventional silicon base materials, but also organic non-siliconeresins such as aromatic resins and polycyclic resins are applicable asthe reversal film-forming material. It then becomes possible to form ahole pattern including both dense and isolated holes through a singleexposure.

[1] A process for forming a pattern by way of positive/negativereversal, comprising the steps of:

coating a chemically amplified positive resist composition onto aprocessable substrate, the resist composition comprising a resincomprising recurring units of structure having acid labile groups whichare eliminatable with acid, the resin turning to be soluble in analkaline developer as a result of elimination of the acid labile groups,a photoacid generator capable of generating an acid upon exposure tohigh-energy radiation and optionally, a thermal acid generator capableof generating an acid upon heating, and an organic solvent, prebakingthe coating to remove the unnecessary solvent and to form a resist film,

exposing the resist film to high-energy radiation through a phase shiftmask including a lattice-like first shifter having a line width equal toor less than half a pitch and a second shifter arrayed on the firstshifter and consisting of lines whose on-wafer size is 2 to 30 nmthicker than the line width of the first shifter, post-exposure bakingso that the acid generated by the acid generator upon exposure may acton acid labile groups in the resin for thereby effecting eliminationreaction of acid labile groups in the resin in exposed areas, developingthe exposed resist film with an alkaline developer to form a positivepattern,

illuminating or heating the positive pattern, the acid generated byillumination or the heat serving to eliminate acid labile groups in theresin in the positive pattern for thereby increasing the alkalinesolubility of the resin and to induce crosslinks in the resin to such anextent that the resin may not lose a solubility in an alkaline wetetchant, for thereby endowing the positive pattern with resistance to anorganic solvent used in a reversal film-forming composition,

coating a reversal film-forming composition on the positivepattern-bearing substrate to form a reversal film, and

dissolving away the crosslinked positive pattern using an alkaline wetetchant.

[2] The process of [1] wherein the second shifter is arrayed on thefirst shifter.

[3] The process of [1] or [2] wherein the second shifter is ofcrisscross or lattice-like shape.

[4] The process of any one of [1] to [3] wherein the step of developingthe exposed resist film is to form a pattern of dots only at theintersections between gratings of the second shifter.

[5] The process of any one of [1] to [4] wherein the lattice-like firstshifter is a halftone phase shift mask having a transmittance of 3 to15%.

[6] The process of any one of [1] to [5] wherein the phase shift maskincludes the first shifter having a line width equal to or less than ⅓of the pitch and the second shifter consisting of lines whose on-wafersize is 2 to 30 nm thicker than the line width of the first shifter.[7] The process of any one of [1] to [6] wherein in the step ofilluminating or heating the positive pattern for increasing the alkalinesolubility of the resin and for endowing the positive pattern withresistance to an organic solvent used in a reversal film-formingcomposition,

the dissolution rate of the crosslinked positive pattern in an alkalinewet etchant is such that the crosslinked positive pattern exhibits anetching rate in excess of 2 nm/sec when etched with 2.38 wt % TMAHaqueous solution,

the organic solvent used in the reversal film-forming composition isselected from the group consisting of propylene glycol monomethyl etheracetate, cyclohexanone, ethyl lactate, propylene glycol monomethylether, propylene glycol monoethyl ether, propylene glycol monopropylether, propylene glycol monobutyl ether, and heptanone, and mixtures oftwo or more of the foregoing,

the resistance to organic solvent of the crosslinked positive pattern issuch that the crosslinked positive pattern experiences a film slimmingof up to 10 nm when contacted with the organic solvent for 30 seconds.

[8] The process of any one of [1] to [7] wherein said reversalfilm-forming composition comprises a resin comprising monomeric units ofaromatic or alicyclic structure.

[9] The process of any one of [1] to [8], further comprising, betweenthe step of coating a reversal film-forming composition on the positivepattern-bearing substrate to form a reversal film and the step ofdissolving away the crosslinked positive pattern using an alkaline wetetchant, the step of removing the reversal film deposited on thecrosslinked positive pattern.[10] The process of [9] wherein the step of removing the reversal filmdeposited on the crosslinked positive pattern includes wet etching.[11] The process of [10] wherein the reversal film is soluble in analkaline wet etchant, but has a dissolution rate which is slower thanthat of the crosslinked positive pattern after the step of endowing thepositive pattern with resistance to organic solvent, the wet etchinguses an alkaline wet etchant, and the step of removing the reversal filmdeposited on the crosslinked positive pattern and the step of dissolvingaway the crosslinked positive pattern are concurrently carried out.[12] The process of [11] wherein the reversal film has a dissolutionrate of 0.02 nm/sec to 2 nm/sec when etched with 2.38 wt % TMAH aqueoussolution.[13] The process of any one of [1] to [12] wherein said chemicallyamplified positive resist composition comprises a component capable ofgenerating an acid in the step of heating for endowing the positivepattern with organic solvent resistance.[14] The process of [13] wherein the component capable of generating anacid is a thermal acid generator which is added to the resistcomposition in addition to the photoacid generator.[15] The process of [14] wherein the thermal acid generator has thegeneral formula (P1a-2):

wherein R^(101d), R^(101e), R^(101f), and R^(101g) are eachindependently hydrogen, a straight, branched or cyclic C₁-C₁₂ alkyl,alkenyl, oxoalkyl or oxoalkenyl group, a C₆-C₂₀ aryl group, or a C₇-C₁₂aralkyl or aryloxoalkyl group, in which some or all hydrogen atoms maybe substituted by alkoxy groups, or R^(101d) and R^(101e), or R^(101d),R^(101e) and R^(101f) may bond together to form a ring with the nitrogenatom to which they are attached, each of R^(101e) and R^(101f) or eachof R^(101d), and R^(101e) and R^(101f) is a C₃-C₁₀ alkylene group or ahetero-aromatic ring having incorporated therein the nitrogen atom whenthey form a ring, and K⁻ is a sulfonate having at least one α-positionfluorinated, perfluoroalkylimidate or perfluoroalkylmethidate.[16] The process of any one of [1] to [15] wherein in said chemicallyamplified positive resist composition, the resin comprises recurringunits having a lactone ring and recurring units having an acid labilegroup which is eliminatable with acid.[17] The process of any one of [1] to [16] wherein in said chemicallyamplified positive resist composition, the resin comprises anelectrophilic partial structure such as an ester group or cyclic etherwhich will form crosslinks in the resin of the positive resist pattern.[18] The process of [17] wherein in said chemically amplified positiveresist composition, the resin comprises recurring units having a7-oxanorbornane ring and recurring units having an acid labile groupwhich is eliminatable with acid, and heat is applied in the step ofilluminating the positive pattern to generate an acid wherebyelimination of acid labile groups and crosslinking of the resin takeplace simultaneously in the positive pattern.[19] The process of [18] wherein the recurring units having a7-oxanorbornane ring are recurring units (a) having the general formula(1):

wherein R¹ is hydrogen or methyl, R² is a single bond or a straight,branched or cyclic C₁-C₆ alkylene group which may have an ether or esterradical, and which has a primary or secondary carbon atom through whichit is linked to the ester group in the formula, R³, R⁴, and R⁵ are eachindependently hydrogen or a straight, branched or cyclic C₁-C₆ alkylgroup, and “a” is a number in the range: 0<a<1.0.[20] The process of any one of [16] to [19] wherein the recurring unitshaving an acid labile group which is eliminatable with acid arerecurring units (b) having the general formula (2):

wherein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is anumber in the range: 0<b≦0.8.[21] The process of [20] wherein the acid labile group of R⁷ is an acidlabile group of alicyclic structure which is eliminatable with acid.[22] The process of any one of [1] to [21] wherein the positive patterncomprises a dot pattern, and the pattern resulting frompositive/negative reversal comprises a hole pattern.[23] The process of any one of [1] to [22] wherein the positive patterncomprises both a dense dot pattern and an isolated dot pattern, and thepattern resulting from positive/negative reversal comprises both a densehole pattern and an isolated hole pattern.[24] The process of [23] wherein a dense dot pattern and an isolated dotpattern are formed as the positive pattern by exposure to a dense dotpattern and subsequent exposure to an unnecessary portion of the dotpattern, and a dense hole pattern and an isolated hole pattern areformed by positive/negative reversal therefrom.[25] A process for forming a pattern by way of positive/negativereversal according to [1], comprising the steps of:

coating a chemically amplified positive resist composition onto aprocessable substrate, said resist composition comprising a resincomprising recurring units having acid labile groups which areeliminatable with acid, a photoacid generator capable of generating anacid upon exposure to high-energy radiation and a solvent, heating toremove the unnecessary solvent to form a resist film,

coating a protective film-forming composition onto the resist film anddrying to form a protective film,

exposing the resist film to high-energy radiation in a repeating densepattern from a projection lens, by immersion lithography with water or atransparent liquid having a refractive index of at least 1 interveningbetween the resist film and the projection lens, further exposing anunnecessary region of the dense pattern or unexposed area by immersionlithography, post-exposure baking for causing the acid generated by theacid generator upon exposure to act on the acid labile groups on theresin whereby the acid labile groups on the resin in the exposed areaundergo elimination reaction, and developing the exposed resist filmwith an alkaline developer to form a positive pattern,

treating the positive pattern so as to eliminate the acid labile groupson the resin in the positive pattern resulting from the previous step,and to induce crosslinking in the resin to such an extent that the resinmay not lose a solubility in an alkaline wet etchant, for therebyendowing the positive pattern with resistance to an organic solvent tobe used in a reversal film-forming composition,

coating a reversal film-forming composition thereon to form a reversalfilm, and

dissolving away the positive pattern using an alkaline wet etchant.

[26] The process of [25] wherein said protective film-formingcomposition is based on a copolymer comprising amino-containingrecurring units.

[27] The process of [25] or [26] wherein said protective film-formingcomposition further comprises an amine compound.

[28] The process of any one of [1] to [27], further comprising the stepsof forming a carbon film having a carbon content of at least 75% byweight on the processable substrate, forming a silicon-containingintermediate film thereon, and coating a resist composition forpositive/negative reversal thereon, the reversal film being formed of ahydrocarbon-based material.[29] The process of any one of [1] to [27], further comprising the stepsof forming a carbon film having a carbon content of at least 75% byweight on the processable substrate, and coating a resist compositionfor positive/negative reversal thereon, the reversal film being formedof a silicon-containing material.[30] The process of [29], further comprising the steps of forming acarbon film having a carbon content of at least 75% by weight on theprocessable substrate, forming an organic antireflection film thereon,and coating a resist composition for positive/negative reversal thereon,the reversal film being formed of a silicon-containing material.

FIG. 5 illustrates an aperture configuration in a dipole illuminationexposure tool applied in combination with a mask of Y-direction linepattern as shown in FIG. 6. FIG. 7 illustrates an aperture configurationin a dipole illumination exposure tool applied in combination with amask of X-direction line pattern as shown in FIG. 8. The shape ofopening may be circular as shown in FIG. 5, elliptic as shown in FIG. 9,or arc as shown in FIG. 10.

FIG. 11 illustrates an optical image of Y-direction lines having a pitchof 80 nm and a line size of 40 nm printed using ArF excimer laser of 193nm wavelength, NA 1.3 lens, dipole illumination, 6% halftone phase shiftmask, and s-polarization. FIG. 12 illustrates an optical image ofX-direction lines having a pitch of 80 nm and a line size of 40 nmprinted using ArF excimer laser of 193 nm wavelength, NA 1.3 lens,dipole illumination, 6% halftone phase shift mask, and s-polarization. Ablack area corresponds to a light-shielded region and a white areacorresponds to an intense light region. FIG. 13 is a contrast imageobtained by overlaying the optical image of X-direction lines on that ofY-direction lines. Against the expectation that a combination of X and Ylines may form a lattice-like image, weak light areas draw circularfigures. As the size of a circle increases, the figure approaches torhombus, tending to merge with adjacent figures. As the size of a circlebecomes smaller, circularity is improved.

FIG. 14 illustrates a simulation of a pattern profile of a resist filmon the basis of the optical image of FIG. 13. Herein, Z direction is thenegative of logarithm of a dissolution rate of the resist film,reflecting the pattern profile of the resist film. It is shown that a80-nm pitch dot pattern of the positive resist film can be formed usingthe double dipole lithography including two exposures of X and Y lines.

FIG. 15 illustrates the layout of a mask having a lattice-like patternconsisting of X and Y lines. A black area is a halftone shifter.

FIG. 16 illustrates an aperture configuration employed in cross-poleillumination corresponding to the lattice-like mask pattern of X and Ylines.

FIG. 17 is a simulation of an optical image of a lattice-like patternhaving a pitch of 90 nm and a line width of 20 nm as on-wafer size,under conditions: ArF excimer laser of 193 nm wavelength, NA 1.3 lens,cross-pole illumination, 6% halftone phase shift mask (of the layoutshown in FIG. 15), and azimuthally polarized illumination. FIG. 18 is aresist profile simulation. The resist used herein has a sensitivity of30 mJ/cm².

FIG. 19 is a simulation of an optical image of a lattice-like patternhaving a pitch of 90 nm and a line width of 25 nm. FIG. 20 is a resistprofile simulation. The resist used herein has a sensitivity of 50mJ/cm².

FIG. 21 is a simulation of an optical image of a lattice-like patternhaving a pitch of 90 nm and a line width of 30 nm. FIG. 22 is a resistprofile simulation. The resist used herein has a sensitivity of 80mJ/cm².

As the width of lines in the lattice-like pattern increases, theintensity of light in the light-shielding portion is reduced, thesensitivity of resist becomes lower, and the film retention of dotpattern is increased.

FIG. 23 is a resist profile simulation of a lattice-like pattern havinga pitch of 90 nm and a line width of 20 nm in an exposure dose of 50mJ/cm². FIG. 24 is a resist profile simulation of the same lattice-likepattern in an exposure dose of 80 mJ/cm². It is seen that on use ofmasks of lattice-like pattern having a line width of 20 nm and 25 nm, ifthe optimum exposure dose is matched with that for the line width of 25nm, the pattern corresponding to the line width of 20 nm is not formedbecause it is entirely dissolved. This is also true when masks oflattice-like pattern having a line width of 20 nm and 30 nm are used.

A thin lattice-like pattern is formed on the entire surface of a mask,and a thick lattice-like or cross pattern is located where a dot patternis to be formed. No dots are formed at thin gratings, but dots areformed only at thick gratings. The thin lattice-like pattern functionsas an auxiliary pattern for increasing the contrast of the thicklattice-like pattern. This permits both a dense pattern and an isolatedpattern to be formed through a single exposure in a common exposuredose.

As shown in FIG. 25, on a lattice-like pattern having a pitch of 90 nmand a line width of 20 nm, thick crisscross or intersecting linesegments are disposed where dots are to be formed. A black areacorresponds to the halftone shifter portion. Line segments with a widthof 30 nm are disposed in the dense pattern portion whereas thicker linesegments (width 40 nm in FIG. 25) are disposed in more isolated patternportions. Since the isolated pattern provides light with a lowerintensity than the dense pattern, thicker line segments are used. Sincethe peripheral area of the dense pattern provides light with arelatively low intensity, line segments having a width of 32 nm areassigned to the peripheral area which width is slightly greater thanthat in the internal area of the dense pattern.

FIG. 26 shows an optical image from the mask of FIG. 25. Black or inkedareas are where dots of the resist pattern are formed. Black spots arefound at positions other than where dots are formed, but few aretransferred in practice because they are of small size. Optimizationsuch as reduction of the width of grating lines corresponding tounnecessary dots can inhibit transfer of unnecessary dots. FIG. 27illustrates a resist profile simulation based on the optical image ofFIG. 26. It is demonstrated that both dense dots and isolated dots canbe formed at an exposure dose of 70 mJ/cm².

When dots are formed by the prior art method, a mask having a dotpattern is used. FIG. 28 shows the layout of a mask having a dotpattern. Black areas are halftone shifters. The pattern size forisolated dots is greater than that for dense dots, which reducesproximity bias. Squares for dense dots have one side with a size of 55nm whereas squares for isolated dots have one side with a size of 90 nm,indicating a bias of 35 nm. In contrast, the mask pattern of FIG. 25includes dense dot-forming lines having a size of 30 nm and isolateddot-forming lines having a width of 40 nm, with a bias of 10 nm. Sincethe optimum bias varies with the properties of resist as well, it isadvantageous that the mask bias is as small as possible.

FIG. 29 shows an optical image from the mask of FIG. 28. No black spotsare present in the light-shielded portion of FIG. 29, indicating lowerlight-shielding property than the image of FIG. 26. FIG. 30 illustratesa resist profile computed on the basis of the optical image of FIG. 29.The film retention of dot pattern is reduced as compared with FIG. 27,which is accounted for by the absence of a strongly light-shieldedportion in FIG. 29. A reduction in film retention of dot pattern raisesthe problem that when a reversal film is coated thereon and treated forreversal, reversal dissolution does not proceed.

The pack and unpack (PAU) method involves coating a positive resistfilm, first exposure to form a dense hole pattern, coating thereon anegative resist film material in water or alcohol solvent which does notdissolve the positive resist pattern, and second exposure for erasing anunnecessary hole pattern portion. Since a dense hole pattern withuniform size is initially formed, the PAU method is also devoid ofproximity bias. Since the first exposure is exposure of a hole pattern,the PAU method is not improved in resolution over the conventionalexposure method and only proximity bias is eliminated. In contrast, thepattern forming process of the invention permits both dense and isolateddot patterns to be formed through a single exposure using a mask havinga high contrast lattice-like line pattern, and is thus significantlyimproved in resolution over the conventional hole forming method andalso in throughput over the PAU method involving two exposures.

ADVANTAGEOUS EFFECTS OF INVENTION

As compared with the method of forming fine holes by combining thedouble dipole lithography with a negative resist film, the patternforming process of the invention is capable of forming a hole pattern byusing a positive resist film, effecting a single exposure to form a dotpattern at the same level of resolution as the double dipolelithography, and effecting positive/negative reversal to form the holepattern. Use of a positive resist film which has a higher resolutioncapability than a negative resist film offers improvements in resolutionand process margins such as focus margin and exposure margin. Sincepositive/negative reversal is carried out by wet etching with adeveloper, the process achieves a high throughput as compared with theconventional dry development and eliminates a need for an etching systemfor dry development. Although the double dipole lithography needs twomasks, the inventive process uses a single phase shift mask having alattice-like pattern of lines with different width. Additionally, theprocess achieves a level of resolution equivalent to the double dipolelithography and permits both dense and isolated patterns to be formedthrough a single exposure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates in cross-sectional views a prior artprocess for forming a hole pattern through exposure of a positivephotoresist material, FIG. 1A shows formation of a photoresist film,FIG. 1B shows exposure and development of the photoresist film, and FIG.1C shows etching of a processable substrate.

FIG. 2 schematically illustrates in cross-sectional views a prior artimage reversal process using a positive i or g-line resist materialbased on a quinonediazide-novolac resin, FIG. 2A shows formation of aphotoresist film, FIG. 2B shows exposure and heating of the photoresistfilm, FIG. 2C shows flood exposure, FIG. 2D shows pattern reversal bydevelopment, and FIG. 2E shows etching of a processable substrate.

FIG. 3 schematically illustrates in cross-sectional views a prior artimage reversal process involving hardening of a developed resist filmand burying of SOG film, FIG. 3A shows formation of a photoresist film,FIG. 3B shows exposure and development of the photoresist film, FIG. 3Cshows crosslinking of the photoresist film, FIG. 3D shows coating of aSOG film, FIG. 3E shows light etching with CMP or CF gas, FIG. 3F showspattern reversal by oxygen/hydrogen gas etching, and FIG. 3G showsetching of a processable substrate.

FIG. 4 schematically illustrates in cross-sectional views the patternforming process of the invention, FIG. 4A shows that a processablesubstrate and a resist film are disposed on a substrate, FIG. 4B showsthat the resist film is exposed and developed, FIG. 4C shows that theresist pattern is deprotected and crosslinked under the action of acidand heat, FIG. 4D shows that a pattern reversal film is coated, FIG. 4Eshows that the pattern reversal film is developed for positive/negativereversal, and FIG. 4F shows that the processable substrate is etchedusing the positive/negative reversal pattern.

FIG. 5 illustrates an aperture configuration in an exposure tool used inY dipole illumination exposure.

FIG. 6 illustrates a Y-direction line pattern of the mask used in Ydipole illumination.

FIG. 7 illustrates an aperture configuration in an exposure tool used inX dipole illumination exposure.

FIG. 8 illustrates a X-direction line pattern of the mask used in Ydipole illumination.

FIG. 9 illustrates apertures of elliptic shape in an exposure tool usedin Y dipole illumination exposure.

FIG. 10 illustrates apertures of arc shape in an exposure tool used in Ydipole illumination exposure.

FIG. 11 illustrates a light intensity distribution under conditions: NA1.3 lens, dipole illumination, s-polarized illumination, and 6% halftonephase shift mask of Y-direction lines, wherein a darker inked areaindicates a weaker light intensity.

FIG. 12 illustrates a light intensity distribution under conditions: NA1.3 lens, dipole illumination, s-polarized illumination, and 6% halftonephase shift mask of X-direction lines, wherein a darker inked areaindicates a weaker light intensity.

FIG. 13 illustrates a light intensity distribution of double dipoleexposure obtained by overlaying the X-direction lines of FIG. 12 on theY-direction lines of FIG. 11 both with NA 1.3 lens, wherein a darkerinked area indicates a weaker light intensity.

FIG. 14 illustrates a simulation of a resist profile of double dipoleillumination lithography with NA 1.3 lens wherein Z axis is the negativeof logarithm of a dissolution rate of the resist, reflecting the resistprofile of dot pattern, and the exposure dose is 20 mJ/cm².

FIG. 15 illustrates a lattice-like mask pattern of X and Y lines whereina black area is a halftone shifter.

FIG. 16 illustrates an aperture configuration in a cross-poleillumination exposure tool applied to the mask of X-Y line lattice-likepattern.

FIG. 17 is a simulation of an optical image of a lattice-like patternhaving a pitch of 90 nm and a line width of 20 nm under conditions: NA1.3 lens, cross-pole illumination, 6% halftone phase shift mask, andazimuthally polarized illumination.

FIG. 18 is a resist profile simulation corresponding to the opticalimage of FIG. 17 wherein the exposure dose is 30 mJ/cm².

FIG. 19 is a simulation of an optical image of a lattice-like patternhaving a pitch of 90 nm and a line width of 25 nm under conditions: NA1.3 lens, cross-pole illumination, 6% halftone phase shift mask, andazimuthally polarized illumination.

FIG. 20 is a resist profile simulation corresponding to the opticalimage of FIG. 19 wherein the exposure dose is 50 mJ/cm².

FIG. 21 is a simulation of an optical image of a lattice-like patternhaving a pitch of 90 nm and a line width of 30 nm under conditions: NA1.3 lens, cross-pole illumination, 6% halftone phase shift mask, andazimuthally polarized illumination.

FIG. 22 illustrates a resist profile simulation corresponding to theoptical image of FIG. 21 wherein the exposure dose is 80 mJ/cm².

FIG. 23 illustrates a resist profile simulation corresponding to theoptical image of FIG. 17 wherein the exposure dose is 50 mJ/cm².

FIG. 24 illustrates a resist profile simulation corresponding to theoptical image of FIG. 17 wherein the exposure dose is 80 mJ/cm².

FIG. 25 illustrates a lattice-like mask pattern of X and Y lines havinga dot pattern disposed thereon, wherein black areas are 6% halftoneshifters.

FIG. 26 is an optical image produced under conditions: NA 1.3 lens,cross-pole illumination, azimuthally polarized illumination, andhalftone phase shift mask of FIG. 25.

FIG. 27 illustrates a resist profile simulation corresponding to theoptical image of FIG. 26.

FIG. 28 illustrates a dot mask pattern including dots of different sizewherein black areas are 6% halftone shifters.

FIG. 29 is an optical image produced under conditions: NA 1.3 lens,cross-pole illumination, azimuthally polarized illumination, and 6%halftone phase shift mask of FIG. 28.

FIG. 30 illustrates a resist profile simulation corresponding to theoptical image of FIG. 29.

FIG. 31 illustrates a mask pattern in which arrowed lattice-likeshifters (and dots) are staggered.

FIG. 32 illustrates a resist profile simulation produced underconditions: NA 1.3 lens, cross-pole illumination, azimuthally polarizedillumination, and mask of the layout of FIG. 25 having the same linewidth and a reduced pitch of 80 nm.

FIG. 33 illustrates a resist profile simulation produced underconditions: NA 1.3 lens, cross-pole illumination, azimuthally polarizedillumination, and mask of the layout of FIG. 28 having the same linewidth and a reduced pitch of 80 nm.

FIG. 34 illustrates a mask pattern used in Examples 1 and 2 and alsoindicates size measuring positions in a corresponding resist pattern.

FIG. 35 illustrates a mask pattern used in Comparative Example 1 andalso indicates size measuring positions in a corresponding resistpattern.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The terms “a” and “an” herein do not denote a limitation of quantity,but rather denote the presence of at least one of the referenced item.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

As used herein, the notation (C_(n)-C_(m)) means a group containing fromn to m carbon atoms per group.

The abbreviations and acronyms have the following meaning.

Mw: weight average molecular weight

Mn: number average molecular weight

Mw/Mn: molecular weight distribution or dispersity

GPC: gel permeation chromatography

PEB: post-exposure baking

CVD: chemical vapor deposition

SOG: spin on glass

TMAH: tetramethylammonium hydroxide

PGMEA: propylene glycol monomethyl ether acetate

The abbreviation “phr” refers to parts by weight per 100 parts by weightof resin or polymer.

The process of the invention includes the step of exposing the resistfilm to high-energy radiation through a phase shift mask having alattice-like halftone shifter pattern. Specifically, the phase shiftmask has a lattice-like halftone shifter pattern in which cross orlattice-like patterns thicker than the width of vertical and horizontalgratings are formed preferably at intersections between vertical andhorizontal gratings. A lattice-like pattern is formed where no dots areto be formed as well, while first shifter gratings where no dots are tobe formed have a thin line width and second shifter gratings where dotsare to be formed have a thick line width. The line width differencebetween the first shifter and the second shifter is 2 to 30 nm,preferably 2 to 20 nm, and more preferably 3 to 15 nm. Preferably thewidth of the first shifter is 5 to 40 nm thinner than the half-pitch.For an array of gratings at a pitch of 90 nm, the first shifter has awidth of about 10 to 20 nm, and the second shifter has a width of about25 to 50 nm. The width of the second shifter is preferably about 25 to35 nm, more preferably about 30 nm in the case of dense patterns, andpreferably about 35 to 45 nm, more preferably about 40 nm in the case ofisolated patterns. The halftone shifters have a transmittance of 3 to15%, preferably 4 to 10%. If the pitches of the first shifter are allthe same, the best contrast improving effect is exerted. Since thesecond shifter must be arrayed on the first shifter, the position ofdots in positive resist is limited to a multiple of the half-pitch ofthe shifter. If dots are formed at positions staggered from the multipleposition of the half-pitch, a mask having some second shifters staggeredfrom the first shifter as indicated by the arrows in FIG. 31 may beused.

On use of a mask of X-Y gratings, the illumination of the exposure toolis most preferably a combination of cross-pole illumination through theapertures shown in FIG. 16 with X-Y polarized illumination. Instead ofX-Y polarized illumination, azimuthally polarized illumination may beemployed. Although the azimuthally polarized illumination is ring-likeannular polarized illumination, its combination with cross-poleillumination with only the outermost periphery of crisscross in X and Ydirections being cut out exerts substantially the same effect as the X-Ypolarized illumination.

Instead of cross-pole illumination, two exposures by X-Y dipoleillumination through the apertures shown in FIGS. 7 and 5, respectively,may be performed. Although the resultant effect is substantially thesame as the cross-pole illumination, the two dipole exposures isdisadvantageous in throughput.

On use of an oblique 45 degree lattice mask, the illumination is acombination of oblique 45 degree cross-pole illumination withazimuthally polarized illumination. Instead of cross-pole illumination,annular illumination may be used in combination with azimuthallypolarized illumination, and hexa-pole or octa-pole illumination may becombined with azimuthally polarized illumination. Alternatively, annularillumination having a small circle or annulus at the center, cross-pole,hexa-pole, or octa-pole illumination may be used. Although polarizedillumination may not be used, a pattern with a finer pitch can be formedusing polarized illumination. A pattern with the finest pitch can beformed from a combination of a X-Y lattice mask, cross-pole illumination(inter alia, the outermost periphery cut out at an angle of up to 35deg, preferably up to 25 deg) and X-Y polarized illumination.

The resolution limit of a line pattern is in principle equal to thewavelength divided by lens' NA and 4. In an example of ArF lithographywith 193 nm wavelength and a NA 1.30 lens, the maximum resolution is37.1 nm. Actually, polarized illumination has a modification which isnot equal to 100%, and the cutout angle of dipole illumination isdifficulty reduced below 20%. It is then impossible to form an idealoptical image. A very fine pattern is largely affected by the resolutioncapability of a resist film. For these reasons, actually the maximumresolution is 38 nm in pinpoint, and the maximum resolution with acertain margin is 39 nm.

Nevertheless, a simulation as shown in FIG. 32 attests that using thepattern forming process of the invention, dots at the same half-pitch of40 nm as lines can be resolved despite two-dimensional pattern. Bothdense and isolated patterns can be formed at the same time through asingle exposure. In FIG. 32, a computation is performed using a maskhaving the same line width as in the mask of FIG. 25, but a pitchreduced from 90 nm to 80 nm. The results of computation of a resistprofile using a mask having the same dot size as in the mask of FIG. 28,but a pitch of 80 nm are shown in FIG. 33. Outstanding film slimming ofisolated patterns and mergence of dense patterns are seen, indicatingthat the desired pattern may not be formed.

As discussed above, several attempts have already been made to form apattern, which is optically disadvantageous to form from a positiveresist material as such, using a positive resist material featuring ahigh resolution capability and positive/negative reversal. There weremany problems to be overcome in the course of development works. In thesituation where a reversal film is formed on a once formed positivepattern, how to deposit a new coating without disrupting the underlyingpattern is one of such problems. The initial approach addressing thisproblem is to use an aqueous composition in which the positive patternis not dissolvable, as the reversal film-forming composition. Thereversal film material which can be used is limited to a narrow range ofwater-soluble materials. Then JP-A 2005-43420 proposes EB curing, bywhich a positive pattern is crosslinked to be insoluble in solvents anddevelopers before a reversal film is formed. Another problem is how toselectively remove the positive pattern relative to the reversal film.Selective removal is achieved using SOG and organic silicone materialshaving resistance to oxygen dry etching as the reversal film as taughtin JP-A 2005-43420.

On the other hand, the fact that a resist film as shown in JP-A2005-43420 is crosslinked and insolubilized upon exposure to high-energyradiation was known at the initial phase of research and development ofchemically amplified resist materials as a phenomenon that occurs when achemically amplified resist film is exposed to radiation of too highenergy. That is, it is a phenomenon that when polyhydroxystyrene unitsof which a chemically amplified resist polymer is composed are exposedto high intensity light, a hydrogen radical is eliminated from themethine to which the phenyl group is bonded, and the resulting radicalacts to form crosslinks between resin molecules whereby the resin isinsolubilized. It is believed that this radical creation capable ofinducing crosslink formation can occur not only on the styrenestructure, but also on the polyacrylic acid structure. It is furtherbelieved that similar crosslink formation occurs on methylene bonded toa heteroatom. However, the inventors observed that when light exposureis made stepwise, insolubilization of a resist film by crosslinkformation does not instantly occur, but past consecutive points of timewhen the dissolution rate is slightly reduced, and attempted to utilizethis phenomenon. More particularly, the initially observed reductions ofdissolution rate are results of crosslinks forming within or betweenmolecules within a limited range. As long as crosslinking is within thelimited range, there is a possibility that resistance to organicsolvents such as the coating solvent is obtainable without completelylosing a dissolution rate in alkaline developer. Then, studying to forma pattern having resistance to organic solvents commonly used infilm-forming compositions without completely losing a dissolution ratein alkaline developer, the inventors have found that such a pattern isfeasible.

If the method of endowing a positive pattern with resistance to organicsolvents without completely losing solubility in alkaline developer asmentioned above is incorporated in the process of forming a resistpattern through positive/negative reversal, a pattern forming processinvolving reversal of a positive pattern to a negative pattern becomespossible as described below. Namely, in accordance with the ordinarypositive pattern forming method, first a chemically amplified positiveresist composition is coated and prebaked to form a resist film. Thenpatternwise exposure is performed, and post-exposure heating or bakingis performed to eliminate acid labile groups from the resin in theexposed area, for thereby turning the exposed area soluble in alkalinedeveloper. This is followed by development with an alkaline developer,yielding a positive pattern. Next, the resulting positive pattern issubjected to the step of endowing the positive pattern with resistanceto an organic solvent to be used in a reversal film-forming compositionwithout completely losing solubility in the alkaline developer. Next, onthe substrate having the positive pattern endowed with resistance to anorganic solvent to be used in a reversal film-forming composition, thereversal film-forming composition in the form of a solution in thatorganic solvent is coated to form a reversal film. At this point, thereversal film is coated so as to completely bury or fill spaces in thepositive pattern, although the reversal film may be coated so as to forma layer over the positive pattern as well. In such an event, asdescribed in JP-A 2001-92154 and JP-A 2005-43420, after the reversalfilm is formed, the portion of the reversal film deposited on thepositive resist is removed and the positive pattern is then removedusing an alkaline wet etchant. Then only the portion of the reversalfilm where the positive pattern is absent is left behind, that is, areversal film pattern reflecting positive/negative reversal is obtained.It is noted that the alkaline wet etchant serves to dissolve thepositive pattern, and the developer for forming the positive pattern maybe used as the etchant while its concentration may be adjusted ifnecessary.

The resist pattern forming process relying on positive/negative reversalaccording to the invention achieves significant simplification ofoperation because the removal of the positive pattern does not needconventional oxygen dry etching. Further, the reversal film which can beused in the process may be any of conventional organic films includingantireflective coatings (ARC) of aromatic organic polymers and organicunderlayer films used in the multilayer resist process, specificallyorganic films comprising resins containing a majority of aromaticstructure-bearing units well-known in the art, for example, novolacresins (see JP-A 2007-171895), polystyrene resins, vinyl ether oracrylic resins containing anthracene or naphthalene rings, andmulti-branched resins (also known as aliphatic polycyclic structureresins) as used in the ArF resist (see JP-A 2006-293298). Of course,these reversal films may be either films which are insolubilized inorganic solvents through crosslink formation during deposition like theARC or films which are not insolubilized in such a manner, as long as adifference in dissolution rate enough to provide an etching selectivitywith respect to the alkaline wet etchant is available between thereversal film and the positive pattern. If these organic material filmsare used, reversal film patterns resulting from reversal can be directlyused as the etching mask for processing metallic silicon and siliconoxide substrates, like the conventional organic resist patterns.Furthermore, as is well known in the art, when organic reversal films asdescribed above are used, films and substrates of silicon nitride,silicon oxynitride, titanium oxide, titanium nitride, germanium oxideand hafnium oxide may be processed as well as the metallic silicon andsilicon oxide substrates.

Furthermore, if the reversal film used is a film having a scarcealkaline solubility as will be described later, the step of removing thereversal film deposited on the positive resist pattern may resort to thestep of dissolving away in an alkaline wet etchant rather thanconventional dry etching and organic solvent stripping techniques. Whenremoval is made by this technique, the reversal film deposited on theresist pattern and the resist pattern can be concurrently removed by asingle operation, achieving a significant step saving to the overallprocess.

The positive pattern is endowed with resistance to an organic solvent tobe used in the reversal film-forming composition without completelylosing solubility in alkaline wet etchant, and then the positive patternis prevented from being dissolved and hence deformed or disrupted duringcoating and formation of the reversal film. This can be achieved byillumination of high-energy radiation of an appropriate energy level, asdiscussed above. Recognizing that the crosslink formation by light orillumination is sometimes difficult to control owing to the tolerance ofillumination dose and the uniformity of illumination, the inventorssought for another crosslink forming technique and discovered that alimited degree of crosslinking just to impart the desired organicsolvent resistance can be achieved by heat. Particularly when a positivepattern obtained from a resist material having units having acrosslinking capability under strong reaction conditions such as lactonestructure is used, the desired control is relatively easily achievableby heat in the presence of acid.

The step of heating the positive pattern for endowing the positivepattern with resistance to an organic solvent to be used in a reversalfilm-forming composition without losing a solubility in an alkaline wetetchant differs in the amount of acid to be generated and the optimumtemperature to be reached by heating, depending on a particular resistmaterial used. Nevertheless, the resist pattern forming process of theinvention may be readily implemented by setting conditions for this stepin accordance with the following measures. Namely, acid is generatedwithin the resist film by illuminating light or high-energy radiationsuch as electron beam (EB) in an appropriate range to the resist filmand then heating, or solely by heating, whereupon the acid is used toeliminate acid labile groups in the resin to impart a solubility inalkaline solution to the resin. At the same time as this treatment,partial crosslinks are formed by light or heat, whereby the resin isendowed with resistance to an organic solvent to be used in a reversalfilm-forming composition. Preferably, the measure of solubility of theresist film to be achieved by this step is that the resist film has anetching rate in excess of 2 nm/sec when etched with a 2.38 wt % TMAHaqueous solution commonly used in the alkaline development of resistfilms. Also, the resistance to an organic solvent to be used in areversal film-forming composition is of such order that the resistpattern after the resistance-endowing (or crosslinking) treatmentexperiences a thickness reduction of up to 10 nm when contacted with asolvent to be used in a reversal film-forming composition for 30 secondsand more preferably for 60 seconds, and the solvent resistance of suchorder prevents the occurrence of the problem that the pattern of thepositive resist film is fatally damaged when the reversal film-formingcomposition is coated thereon, and hence, a reversed (negative) patternof the desired configuration is not obtainable. It is noted that indetermining the treatment conditions, if a bulk film is used which haspassed the above-described sequence of steps including resist coating,prebaking, and PEB, but excluding only pattern exposure for positivepattern formation, and has further been subjected to a set of conditionsconstituting a candidate step of endowing the positive pattern withresistance to an organic solvent to be used in a reversal film-formingcomposition without losing a solubility in an alkaline wet etchant, thenthe two dissolution rates described above are readily determined.

The organic solvent used in the reversal film-forming composition whichallows for advantageous use of the invention may encompass thosesolvents in which reversal film-forming organic polymers are fullysoluble, and which offer good coating properties, for example, theabove-described hydroxy-bearing solvents, esters, ketones and the like.Specifically, the solvent is selected from among PGMEA, cyclohexanone,ethyl lactate, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, propylene glycol monopropyl ether, propylene glycolmonobutyl ether, and heptanone, which may be used alone or in admixtureof two or more. If desired, alcohols of 3 to 10 carbon atoms, toluene,xylene, anisole or the like may be added to one or more of the foregoingsolvents. Then as to the measure of endowing resistance to the organicsolvent used in the reversal film-forming composition, the resistpattern which has been treated to have such a degree of solventresistance as to experience a thickness reduction (or film slimming) ofup to 10 nm when contacted with a single solvent or a mixture ofsolvents selected from the above-mentioned group for 30 seconds and morepreferably for 60 seconds is particularly preferred because of versatileuse.

When partial crosslinks are induced by illumination of high-energyradiation, the heating treatment of the positive pattern may be heatingto the PEB temperature used in forming the positive pattern or somewhatlower temperature, because the only reaction to be induced by heating isdecomposition of acid labile groups. However, when high-energy radiationis not used, or when the main purpose of high-energy radiation is togenerate acid, that is, when an energy amount equivalent to that ofpattern exposure in the previous step is used and crosslinks are formedmainly by thermally induced reaction, it is preferable to select ahigher temperature than the prebaking temperature used in formation ofthe resist film or the PEB temperature. In the case of a material forwhich this temperature is set lower than the heating of the previousstep, there is a risk of the positive resist film decreasing itsresolution.

The positive/negative reversal process is advantageously utilized in thefollowing case. As for the positive pattern, a finer size pattern can beformed with an over-exposure dose. Then, although it is technicallyquite difficult to form isolated spaces (trench pattern) below theexposure limit, for example, a very fine trench pattern can be formed byutilizing over-dose exposure to form a finer size pattern below theordinary exposure limit and reversing the resulting pattern inaccordance with the inventive process. Moreover, although formation of afine hole pattern encounters more technical difficulty than the trenchpattern, holes of a very small size can be formed by utilizing over-doseexposure to form a fine dot pattern and reversing the resulting patternin accordance with the inventive process.

Now referring to one typical embodiment of the invention wherein amaterial having a scarce solubility in an alkaline wet etchant is usedas the reversal film, the invention is described in further detail. Asused herein, the term “alkaline wet etchant” is substantially equivalentto an alkaline developer used in the development of resist patterns andthus often referred to as “alkaline developer” as well.

In the most preferred embodiment of the invention, the pattern formingprocess comprises the steps of coating a positive resist compositiononto a substrate, said resist composition comprising a polymer (or baseresin) comprising recurring units, preferably of alicyclic structure,having acid labile groups which are eliminatable with acid, the polymerturning, as a result of elimination of acid labile groups andcrosslinking, into a crosslinked polymer having a dissolution rate inexcess of 2 nm/sec in an alkaline developer, prebaking the resistcomposition to form a resist film, exposing a selected portion of theresist film to high-energy radiation, PEB, and developing the exposedresist film with the alkaline developer to form a positive pattern.Thereafter, the positive pattern is treated so as to generate acid andheated, thereby eliminating acid labile groups from the polymer andinducing crosslinking in the polymer in the positive pattern. Then, areversal film having a dissolution rate of 0.02 nm/sec to 2 nm/sec inthe alkaline developer is formed on the substrate to cover the resistpattern. The alkaline developer is then applied thereon to dissolve asurface layer of the reversal film and dissolve away the resist pattern,providing the reversal film with a pattern which is a reversal of theresist pattern.

In this embodiment, a hole pattern can be formed by forming a dotpattern as the resist pattern, followed by reversal.

Preferably crosslink formation is attributed to electrophilic structuressuch as ester groups and cyclic ethers in the resin. Under the action ofacid and heat, crosslinking reaction takes place by reactions such asester exchange, ring-opening, esterification and etherification oflactone ring, or ring-opening, etherification and esterification ofcyclic ethers.

Resist Composition

The positive resist composition used in the pattern forming processcomprises a base resin. A polymer comprising recurring units havinglactone ring, specifically recurring units having 7-oxanorbornane ring,and preferably recurring units having the general formula (1) is usefulas the base resin. The polymer having formula (1) is highly reactive incrosslinking reaction because both ester group and cyclic ether arecontained in a common recurring unit. Since this unit also serves as anadhesive unit, advantageously the base resin is amenable to the patternforming process without further incorporating additional units into theresin.

Herein R¹ is hydrogen or methyl. R² is a single bond, or a straight,branched or cyclic C₁-C₆ alkylene group which may have an ether or esterradical. When R² is alkylene, the alkylene has a primary or secondarycarbon atom bonded to the ester group in the formula. R³, R⁴, and R⁵ areeach hydrogen or a straight, branched or cyclic C₁-C₆ alkyl group. Thesubscript “a” is a number in the range: 0<a<1.0.

Exemplary C₁-C₆ alkylene groups include methylene, ethylene,n-propylene, isopropylene, n-butylene, isobutylene, sec-butylene,n-pentylene, isopentylene, cyclopentylene, n-hexylene, andcyclohexylene.

Exemplary C₁-C₆ alkyl groups include methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, sec-butyl, n-pentyl, isopentyl, cyclopentyl, n-hexyl,and cyclohexyl.

Those monomers Ma from which recurring units (a) having formula (1) arederived have the following formula wherein R¹ to R⁵ are as definedabove.

Examples of monomers Ma are given below.

In the inventive process, once the first pattern is formed via exposureand development, deprotection of acid labile groups and crosslinkage areinduced by the action of acid and heat. Then a film having anappropriate alkaline solubility (reversal film) is coated thereon andalkaline developed.

Subsequent to illumination and heating, the first pattern turns to afilm which is alkaline soluble as a result of deprotection of acidlabile groups in the acid labile group-containing recurring units andwhich is insoluble in a solvent (i.e., solvent in a reversalfilm-forming composition) as a result of crosslinking of 7-oxanorbornanering. Thus, when a pattern reversal film-forming composition having afilm-forming material dissolved in an organic solvent is coated on thefirst pattern, intermixing of the first pattern with the patternreversal film-forming material is avoided.

The reversal film is then treated with an alkaline developer. When asurface portion of the reversal film is dissolved away to the level ofthe first pattern, dissolution of the first pattern starts. Imagereversal occurs in this way.

When a polymer comprising recurring units having oxirane or oxetane isused as the base resin, it does not function as a positive resistcomposition as desired in the invention because the oxirane or oxetanering has so high a rate of acid-assisted cleavage reaction that thepolymer may undergo crosslinking at resist processing temperatures, forexample, at 90 to 130° C. during PEB, and thus become alkali insoluble.In contrast, the 1,4-epoxy bond of 7-oxanorbornane ring is low reactivein acid-assisted cleavage reaction as compared with the oxirane oroxetane ring so that the polymer may not undergo crosslinking in theheating temperature range of PEB. Recurring units having 7-oxanorbornanering are stable relative to acid in the course from coating todevelopment and exert as a hydrophilic group a function of improvingadhesion and alkaline solubility. However, under the impetus of the acidgenerated by flood exposure or heating of the developed pattern andheating at 170° C. or higher, ring opening of the 1,4-epoxy bond of7-oxanorbornane ring occurs and crosslinking reaction takes place,leading to insolubility in the solvent. At the same time, deprotectionof acid labile groups in the acid labile group-containing recurringunits occurs under the impetus of acid and heat, leading to an increasedalkaline solubility. For generating acid, a thermal acid generator maybe added to the resist composition or the surface of the developedpattern may be subjected to flood exposure to UV having wavelength ofless than 400 nm.

In the positive resist composition for use in the pattern formingprocess, a polymer comprising crosslinkable recurring units (a) havingthe general formula (1) above and acid labile group-containing recurringunits (b) having the general formula (2) below is preferably used as thebase resin.

Herein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is anumber in the range: 0<b≦0.8.

Those monomers Mb from which recurring units (b) having formula (2) arederived have the following formula wherein R⁶ and R⁷ are as definedabove.

The acid labile group represented by R⁷ in formula (2) may be selectedfrom a variety of such groups, specifically groups of the followingformulae (AL-10) and (AL-11), tertiary alkyl groups of the followingformula (AL-12), and oxoalkyl groups of 4 to 20 carbon atoms, but notlimited thereto.

In formulae (AL-10) and (AL-11), R⁵¹ and R⁵⁴ each are a monovalenthydrocarbon group, typically a straight, branched or cyclic alkyl groupof 1 to 40 carbon atoms, more specifically 1 to 20 carbon atoms, whichmay contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine.The subscript “a5” is an integer of 0 to 10, and especially 1 to 5. R⁵²and R⁵³ each are hydrogen or a monovalent hydrocarbon group, typically astraight, branched or cyclic C₁-C₂₀ alkyl group, which may contain aheteroatom such as oxygen, sulfur, nitrogen or fluorine. Alternatively,a pair of R⁵² and R⁵³, R⁵² and R⁵⁴, or R⁵³ and R⁵⁴, taken together, mayform a ring, specifically aliphatic ring, with the carbon atom or thecarbon and oxygen atoms to which they are attached, the ring having 3 to20 carbon atoms, especially 4 to 16 carbon atoms.

In formula (AL-12), R⁵⁵, R⁵⁶ and R⁵⁷ each are a monovalent hydrocarbongroup, typically a straight, branched or cyclic C₁-C₂₀ alkyl group,which may contain a heteroatom such as oxygen, sulfur, nitrogen orfluorine. Alternatively, a pair of R⁵⁵ and R⁵⁶, R⁵⁵ and R⁵⁷, or R⁵⁶ andR⁵⁷, taken together, may form a ring, specifically aliphatic ring, withthe carbon atom to which they are attached, the ring having 3 to 20carbon atoms, especially 4 to 16 carbon atoms.

Illustrative examples of the groups of formula (AL-10) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl and2-tetrahydrofuranyloxycarbonylmethyl as well as substituent groups ofthe following formulae (AL-10)-1 to (AL-10)-10.

In formulae (AL-10)-1 to (AL-10)-10, R⁵⁸ is each independently astraight, branched or cyclic C₁-C₈ alkyl group, C₆-C₂₀ aryl group orC₇-C₂₀ aralkyl group; R⁵⁹ is hydrogen or a straight, branched or cyclicC₁-C₂₀ alkyl group; R⁶⁰ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group;and “a5” is an integer of 0 to 10.

Illustrative examples of the acetal group of formula (AL-11) includethose of the following formulae (AL-11)-1 to (AL-11)-34.

Other examples of acid labile groups include those of the followingformula (AL-11a) or (AL-11b) while the polymer may be crosslinked withinthe molecule or between molecules with these acid labile groups.

Herein R⁶¹ and R⁶² each are hydrogen or a straight, branched or cyclicC₁-C₈ alkyl group, or R⁶¹ and R⁶², taken together, may form a ring withthe carbon atom to which they are attached, and R⁶¹ and R⁶² are straightor branched C₁-C₈ alkylene groups when they form a ring. R⁶³ is astraight, branched or cyclic C₁-C₁₀ alkylene group. Each of b5 and d5 is0 or an integer of 1 to 10, preferably 0 or an integer of 1 to 5, and c5is an integer of 1 to 7. “A” is a (c5+1)-valent aliphatic or alicyclicsaturated hydrocarbon group, aromatic hydrocarbon group or heterocyclicgroup having 1 to 50 carbon atoms, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some of thehydrogen atoms attached to carbon atoms may be substituted by hydroxyl,carboxyl, carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or—NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkanetriyl and alkanetetraylgroups, and C₆-C₃₀ arylene groups, which may be separated by aheteroatom such as oxygen, sulfur or nitrogen or in which some of thehydrogen atoms attached to carbon atoms may be substituted by hydroxyl,carboxyl, acyl groups or halogen atoms. The subscript c5 is preferablyan integer of 1 to 3.

The crosslinking acetal groups of formulae (AL-11a) and (AL-11b) areexemplified by the following formulae (AL-11)-35 through (AL-11)-42.

Illustrative examples of the tertiary alkyl of formula (AL-12) includetert-butyl, triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, and tert-amyl groups as well as those of (AL-12)-1to (AL-12)-16.

Herein R⁶⁴ is each independently a straight, branched or cyclic C₁-C₈alkyl group, C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group; R⁶⁵ and R⁶⁷ eachare hydrogen or a straight, branched or cyclic C₁-C₂₀ alkyl group; andR⁶⁶ is a C₆-C₂₀ aryl group or C₇-C₂₀ aralkyl group.

With R⁶⁸ representative of a di- or poly-valent alkylene or arylenegroup included as shown in formulae (AL-12)-17 and (AL-12)-18, thepolymer may be crosslinked within the molecule or between molecules. Informulae (AL-12)-17 and (AL-12)-18, R⁶⁴ is as defined above; R⁶⁸ is astraight, branched or cyclic C₁-C₂₀ alkylene group or arylene group,which may contain a heteroatom such as oxygen, sulfur or nitrogen; andb6 is an integer of 1 to 3.

The groups represented by R⁶⁴, R⁶⁵, R⁶⁶ and R⁶⁷ may contain a heteroatomsuch as oxygen, nitrogen or sulfur. Such groups are exemplified by thoseof the following formulae (AL-13)-1 to (AL-13)-7.

Of the acid labile groups of formula (AL-12), recurring units having anexo-form structure represented by the formula (AL-12)-19 are preferred.

Herein, R⁶⁹ is a straight, branched or cyclic C₁-C₈ alkyl group or asubstituted or unsubstituted C₆-C₂₀ aryl group; R⁷⁰ to R⁷⁵, R⁷⁸ and R⁷⁹are each independently hydrogen or a monovalent hydrocarbon group,typically alkyl, of 1 to 15 carbon atoms which may contain a heteroatom;and R⁷⁶ and R⁷⁷ are hydrogen. Alternatively, a pair of R⁷⁰ and R⁷¹, R⁷²and R⁷⁴, R⁷² and R⁷⁵, R⁷³ and R⁷⁵, R⁷³ and R⁷⁹, R⁷⁴ and R⁷⁸, R⁷⁶ andR⁷⁷, or R⁷⁷ and R⁷⁸, taken together, may form a ring, specificallyaliphatic ring, with the carbon atom(s) to which they are attached, andin this case, each R is a divalent hydrocarbon group, typicallyalkylene, of 1 to 15 carbon atoms which may contain a heteroatom. Also,a pair of R⁷⁰ and R⁷⁹, R⁷⁶ and R⁷⁹, or R⁷² and R⁷⁴ which are attached tovicinal carbon atoms may bond together directly to form a double bond.The formula also represents an enantiomer.

The ester form monomers from which recurring units having an exo-formstructure represented by the formula (AL-12)-19 are derived aredescribed in U.S. Pat. No. 6,448,420 (JP-A 2000-327633).

It is noted that R¹¹¹ and R¹¹² are each independently hydrogen, methyl,—COOCH₃, —CH₂COOCH₃ or the like. Illustrative non-limiting examples ofsuitable monomers are given below.

Also included in the acid labile groups of formula (AL-12) are acidlabile groups having furandiyl, tetrahydrofurandiyl or oxanorbornanediylas represented by the following formula (AL-12)-20.

Herein, R⁸⁰ and R⁸¹ are each independently a monovalent hydrocarbongroup, typically a straight, branched or cyclic C₁-C₁₀ alkyl. R⁸⁰ andR⁸¹, taken together, may form an aliphatic hydrocarbon ring of 3 to 20carbon atoms with the carbon atom to which they are attached. R⁸² is adivalent group selected from furandiyl, tetrahydrofurandiyl andoxanorbornanediyl. R⁸³ is hydrogen or a monovalent hydrocarbon group,typically a straight, branched or cyclic C₁-C₁₀ alkyl, which may containa heteroatom.

Examples of the monomers from which the recurring units substituted withacid labile groups having furandiyl, tetrahydrofurandiyl andoxanorbornanediyl as represented by the formula:

(wherein R⁸⁰ to R⁸³, and R¹¹² are as defined above) are derived areshown below. Note that Me is methyl and Ac is acetyl.

While the polymer used herein preferably includes recurring units (a) offormula (1) and recurring units (b) of formula (2), it may havecopolymerized therein recurring units (c) derived from monomers havingadhesive groups such as hydroxy, cyano, carbonyl, ester, ether groups,lactone rings, carboxyl groups or carboxylic anhydride groups. Examplesof monomers from which recurring units (c) are derived are given below.

Of the recurring units (c), those having an α-trifluoromethyl alcoholgroup or carboxyl group are preferably incorporated in copolymersbecause they improve the alkali dissolution rate of the developedpattern after heating. Examples of recurring units having a carboxylgroup are given below.

In the polymer of the invention, the recurring units (a), (b) and (c)are present in proportions a, b, and c, respectively, which satisfy therange: 0<a<1.0, 0<b≦0.8, 0.1≦a+b≦1.0, 0≦c<1.0, and preferably the range:0.1≦a≦0.9, 0.1≦b≦0.7, 0.2≦a+b≦1.0, and 0≦c≦0.9, provided that a+b+c=1.

It is noted that the meaning of a+b=1 is that in a polymer comprisingrecurring units (a) and (b), the sum of recurring units (a) and (b) is100 mol % based on the total amount of entire recurring units. Themeaning of a+b<1 is that the sum of recurring units (a) and (b) is lessthan 100 mol % based on the total amount of entire recurring units,indicating the inclusion of other recurring units, for example, units(c).

The polymer serving as the base resin in the resist material used in thepattern forming process of the invention should preferably have a weightaverage molecular weight (Mw) in the range of 1,000 to 500,000, and morepreferably 2,000 to 30,000, as measured by GPC using polystyrenestandards. With too low a Mw, the efficiency of thermal crosslinking inthe resist material after development may become low. With too high aMw, the polymer may lose alkaline solubility and have more likelihood offooting after pattern formation.

If a polymer has a wide molecular weight distribution or dispersity(Mw/Mn), which indicates the presence of lower and higher molecularweight polymer fractions, there is a possibility that followingexposure, foreign matter is left on the pattern or the pattern profileis exacerbated. The influences of molecular weight and dispersity becomestronger as the pattern rule becomes finer. Therefore, themulti-component copolymer should preferably have a narrow dispersity(Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide aresist composition suitable for micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity is acceptable.

The polymer as used herein may be synthesized by any desired method, forexample, by dissolving unsaturated bond-containing monomerscorresponding to the respective units (a), (b) and (c) in an organicsolvent, adding a radical initiator thereto, and effecting heatpolymerization. Examples of the organic solvent which can be used forpolymerization include toluene, benzene, tetrahydrofuran, diethyl etherand dioxane. Examples of the polymerization initiator used hereininclude 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours. The acid labile group that has been incorporated in the monomersmay be kept as such, or the acid labile group may be once eliminatedwith an acid catalyst and thereafter protected or partially protected.

As described previously, the pattern forming process of the inventioncomprises the steps of coating the positive resist composition describedabove onto a substrate, prebaking the resist composition to form aresist film, exposing a selected area of the resist film to high-energyradiation, post-exposure baking, and developing the resist film with analkaline developer to dissolve the exposed area thereof to form a resistpattern such as a dot pattern. The subsequent step is to treat theresist pattern (area unexposed to high-energy radiation) so as togenerate an acid, thereby eliminating acid labile groups on the polymer(i.e., deprotection) and inducing crosslinking to the polymer in theresist pattern. In this deprotected and crosslinked state, the polymerhas a dissolution rate in excess of 2 nm/sec, preferably of 3 to 5,000nm/sec, and more preferably 4 to 4,000 nm/sec in an alkaline developer.It is preferred in attaining the objects of the invention that thedissolution rate of the polymer is higher than the dissolution rate ofthe reversal film (to be described later) in the same alkaline developerby a factor of 2 to 250,000, and especially 5 to 10,000.

In order that the polymer have a desired dissolution rate in thedeprotected and crosslinked state, the polymer formulation is preferablydesigned such that the acid labile group-bearing recurring units (b) offormula (2) account for 10 mol % to 90 mol %, and more preferably 12 mol% to 80 mol % of the entire recurring units.

The resist composition used in the pattern forming process of theinvention may further comprise an organic solvent, a compound capable ofgenerating an acid in response to high-energy radiation (known as “acidgenerator”), and optionally, a dissolution regulator, a basic compound,a surfactant, and other components.

The resist composition used herein may include an acid generator inorder for the composition to function as a chemically amplified positiveresist composition. Typical of the acid generator used herein is aphotoacid generator (PAG) capable of generating an acid in response toactinic light or radiation. The PAG may preferably be compounded in anamount of 0.5 to 30 parts and more preferably 1 to 20 parts by weightper 100 parts by weight of the base resin. The PAG is any compoundcapable of generating an acid upon exposure to high-energy radiation.Suitable PAGs include sulfonium salts, iodonium salts,sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acidgenerators. The PAGs may be used alone or in admixture of two or more.Exemplary acid generators are described in U.S. Pat. No. 7,537,880 (JP-A2008-111103, paragraphs [0122] to [0142]).

The resist composition may further comprise one or more of an organicsolvent, basic compound, dissolution regulator, surfactant, andacetylene alcohol. Their examples are described in JP-A 2008-111103.Specifically, exemplary organic solvents are described in paragraphs[0144] to [0145], exemplary basic compounds in paragraphs [0146] to[0164], and exemplary surfactants in paragraphs [0165] to [0166].Exemplary dissolution regulators are described in JP-A 2008-122932 (US2008090172), paragraphs [0155] to [0178], and exemplary acetylenealcohols in paragraphs [0179] to [0182]. The organic solvent may beadded in an amount of 100 to 10,000 parts, and specifically 300 to 8,000parts by weight per 100 parts by weight of the base resin. The basiccompound may be added in an amount of 0.0001 to 30 parts, andspecifically 0.001 to 20 parts by weight per 100 parts by weight of thebase resin.

In an embodiment wherein a thermal acid generator in the form of anammonium salt is added to the photoresist composition in an amount of0.001 to 20 parts, preferably 0.01 to 10 parts by weight per 100 partsby weight of the base resin, an acid can be generated by heating. Inthis embodiment, acid generation, crosslinking reaction and deprotectionreaction of acid labile groups proceed simultaneously. The preferredheating conditions include a temperature of 100 to 300° C., andespecially 130 to 250° C., and a time of 10 to 300 seconds. This resultsin a resist film which meets the necessary properties forpositive/negative reversal including alkaline solubility and solventinsolubility and has an increased mechanical strength sufficient toprevent deformation of the pattern by heating.

Suitable ammonium salts serving as the thermal acid generator includecompounds of the formula (P1a-2).

Herein K⁻ is a sulfonate having at least one fluorine substituted atα-position, or perfluoroalkylimidate or perfluoroalkylmethidate.R^(101d), R^(101e), R^(101f), and R^(101g) are each independentlyhydrogen, a straight, branched or cyclic C₁-C₁₂ alkyl, alkenyl, oxoalkylor oxoalkenyl group, a C₆-C₂₀ aryl group, or a C₁-C₁₂ aralkyl oraryloxoalkyl group, in which some or all hydrogen atoms may besubstituted by alkoxy groups. Alternatively, R^(101d) and R^(101e), orR^(101d), R^(101e) and R^(101f) may bond together to form a ring withthe nitrogen atom to which they are attached, and each of R^(101e) andR^(101f) or each of R^(101d), R^(101e) and R^(101f) is a C₃-C₁₀ alkylenegroup or a hetero-aromatic ring having incorporated therein the nitrogenatom when they form a ring.

Examples of K⁻ include perfluoroalkanesulfonates such as triflate andnonaflate, imidates such as bis(trifluoromethylsulfonyl)imide,bis(perfluoroethylsulfonyl)imide, and bis(perfluorobutylsulfonyl)imide,methidates such as tris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide, and sulfonates having fluorinesubstituted at α-position, represented by the formula (K-1), andsulfonates having fluorine substituted at α-position, represented by theformula (K-2).

In formula (K-1), R¹⁰² is hydrogen, a straight, branched or cyclicC₁-C₂₀ alkyl or acyl group, C₂-C₂₀ alkenyl group or C₆-C₂₀ aryl oraryloxy group, which may have an ether, ester, carbonyl radical orlactone ring and in which some or all hydrogen atoms may be substitutedby fluorine atoms. In formula (K-2), R¹⁰³ is hydrogen, a straight,branched or cyclic C₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group or C₆-C₂₀aryl group.

In a further embodiment, a polymeric additive comprising recurring unitshaving amino and fluoroalkyl groups may be added to the resistcomposition. The polymeric additive may be added in an amount of 0.01 to20 parts, preferably 0.1 to 15 parts by weight per 100 parts by weightof the base resin. The polymeric additive segregates toward the resistfilm surface after coating for eventually preventing a resist pattern asdeveloped from slimming and enhancing the rectangularity thereof. If adot pattern as developed is slimmed or thinned, such slimming mayinterfere with image reversal. Addition of a polymer as shown below iseffective for preventing the pattern film from slimming.

Herein, R⁰¹, R⁰⁴, and R⁰⁷ are each independently hydrogen or methyl. X₁,Y₁ and Y₂ are each independently a single bond, —O—R⁰⁹—, —C(═O)—O—R⁰⁹—or —C(═O)—NH—R⁰⁹—, straight or branched C₁-C₄ alkylene, or phenylenegroup. R⁰⁹ is a straight, branched or cyclic C₁-C₁₀ alkylene group,which may contain an ester (—COO—) or ether (—O—) radical. The subscriptk is 1 or 2. In case of k=1, Y₁ is a single bond, —O—R⁰⁹—, —C(═O)—O—R⁰⁹—or —C(═O)—NH—R⁰⁹—, straight or branched C₁-C₄ alkylene, or phenylenegroup, wherein R⁰⁹ is as defined above. In case of k=2, Y₁ is —O—R¹⁰¹═,—C(═O)—O—R¹⁰¹═ or —C(═O)—NH—R¹⁰¹═, straight or branched C₁-C₄ alkylenegroup with one hydrogen eliminated, or phenylene group with one hydrogeneliminated, wherein R¹⁰¹ is a straight, branched or cyclic C₁-C₁₀alkylene group with one hydrogen atom eliminated, which may contain anester or ether radical. R⁰² and R⁰³ are each independently hydrogen, astraight, branched or cyclic C₁-C₂₀ alkyl group or C₂-C₂₀ alkenyl groupwhich may contain a hydroxyl, ether, ester, cyano, amino radical, doublebond, or halogen atom, or a C₆-C₁₀ aryl group. R⁰² and R⁰³ may bondtogether to form a C₃-C₂₀ ring with the nitrogen atom to which they areattached. R⁰⁵ is a straight, branched or cyclic C₁-C₁₂ alkylene group.R⁰⁶ is hydrogen, fluorine, methyl, trifluoromethyl or difluoromethyl, orR⁰⁶ may bond with R⁰⁵ to form a C₂-C₁₂ aliphatic ring with the carbonatom to which they are attached, which ring may contain an etherradical, fluorinated alkylene or trifluoromethyl radical. R⁰⁸ is astraight, branched or cyclic C₁-C₂₀ alkyl group which is substitutedwith at least one fluorine atom and which may contain an ether, ester orsulfonamide radical. The subscripts d, e-1, and e-2 are numbers in therange: 0<d<1.0, 0≦(e-1)<1.0, 0≦(e-2)<1.0, 0<(e-1)+(e-2)<1.0, and0.5≦d+(e-1)+(e-2)≦1.0.

Reversal Film

On the other hand, the reversal film used has a dissolution rate of 0.02nm/sec to 2 nm/sec, preferably 0.05 nm/sec to 1 nm/sec in an alkalinedeveloper used in the reversal step of the inventive process. Adissolution rate of less than 0.02 nm/sec suggests that the reversalfilm may not be dissolved to the top level of the first resist pattern,resulting in a failure of pattern reversal or a surface layer of thereversed pattern becoming bulged. A dissolution rate of more than 2nm/sec may lead to the disadvantage that the remaining reversal film islessened or the hole size of the reversal pattern is enlarged.

In order that the film surface be adequately dissolved duringdevelopment to form a trench pattern, the alkaline dissolution rate iscontrolled to a range of 0.05 nm/sec to 1 nm/sec. Outside the range, afaster dissolution rate may lead to a greater film slimming duringdevelopment. At a slower dissolution rate, the film surface may not bedissolved, failing to configure a trench pattern. For the purpose oftailoring to an appropriate dissolution rate, units providing analkaline dissolution rate of at least 1 nm/sec and units providing analkaline dissolution rate of up to 0.05 nm/sec are copolymerized.Optimizing the copolymerization ratio leads to a material having anoptimum dissolution rate.

The film (reversal film) used in the pattern forming process and havinga dissolution rate of 0.02 nm/sec to 2 nm/sec in the alkaline developermay be formed of hydrocarbon base materials or silicon-containingmaterials. Preferably used are materials comprising polymers havingphenolic hydroxyl, α-trifluoromethylhydroxyl and carboxyl groups as thebase polymer. The preferred silicon-containing materials are thosehaving silanol groups as well as the foregoing alkali soluble groups.Examples of the polymers having phenolic hydroxyl groups include cresolnovolac resins, phenol oligomers, bisphenol oligomers, bisphenol novolacresins, bisnaphthol oligomers, bisnaphthol novolac resins, calixarene,calix resorcinol, polyhydroxystyrene, polyhydroxyvinylnaphthalene,polyhydroxyindene and copolymers thereof, carboxystyrene polymers,carboxyvinylnaphthalene and copolymers thereof,α-trifluoromethylhydroxy-containing styrene polymers and copolymers,methacrylic acid and carboxyl-containing (meth)acrylate polymers andcopolymers, α-trifluoromethylhydroxy-containing (meth)acrylate polymersand copolymers.

Since most polymers consisting of recurring units having phenolichydroxyl, α-trifluoromethylhydroxyl and carboxyl groups have an alkalinedissolution rate of at least 1 nm/sec, they are copolymerized with unitsproviding an alkaline dissolution rate of up to 0.05 nm/sec. Examples ofsuitable units providing an alkaline dissolution rate of up to 0.05nm/sec include those in which the hydrogen atom of phenolic hydroxyl,α-trifluoromethylhydroxyl or hydroxyl moiety of carboxyl group isreplaced by a C₁-C₂₀ alkyl, C₃-C₂₀ alkenyl, C₆-C₂₀ aryl or acid labilegroup. Also included are styrene, indene, indole, chromone, coumarone,acenaphthylene, norbornadiene, norbornene, vinylnaphthalene,vinylanthracene, vinylcarbazole, vinyl ether derivatives,lactone-containing (meth)acrylates, and hydroxy-containing(meth)acrylates.

More specifically, reactants from which the polymer for use in thereversal film is prepared should have alkali soluble groups such asphenolic hydroxyl, α-trifluoromethylhydroxyl and carboxyl groups.Partial protection of alkali soluble groups or combination thereof withsubstantially alkali insoluble groups is sometimes necessary to tailorthe alkaline dissolution rate.

Suitable polymers having a phenolic hydroxyl group include those novolacresins obtained by reaction of phenol, o-cresol, m-cresol, p-cresol,2,3-dimethylphenol, 2,5-dimethylphenol, 3,4-dimethylphenol,3,5-dimethylphenol, 2,4-dimethylphenol, 2,6-dimethylphenol,2,3,5-trimethylphenol, 3,4,5-trimethylphenol, 2-t-butylphenol,3-t-butylphenol, 4-t-butylphenol, resorcinol, 2-methylresorcinol,4-methylresorcinol, 5-methylresorcinol, catechol, 4-t-butylcatechol,2-methoxyphenol, 3-methoxyphenol, 2-propylphenol, 3-propylphenol,4-propylphenol, 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol,2-methoxy-5-methylphenol, 2-t-butyl-5-methylphenol, pyrogallol, thymol,isothymol, or the like, in the presence of aldehydes. Polymers ofpolymerizable olefin compounds having a phenolic hydroxyl group includepolymers of hydroxystyrene, hydroxyvinylnaphthalene,hydroxyvinylanthracene, hydroxyindene, hydroxyacenaphthylene, and themonomers shown below.

Polymers of monomers from which carboxyl-bearing recurring units arederived may also be used as the material for forming the reversal film.Examples of the monomers are shown below.

For partial protection of phenolic hydroxyl or carboxyl groups for thepurpose of tailoring the alkaline dissolution rate, the hydrogen atom ofthe hydroxyl group or hydroxyl moiety of the carboxyl group ispreferably replaced by a C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₆-C₂₀ aryl,acetyl, pivaloyl or acid labile group. The acid labile group used hereinmay be the same as described above.

For the purpose of tailoring the alkaline dissolution rate,substantially alkali insoluble recurring units (s-3) may also becopolymerized. Examples of the substantially alkali insoluble recurringunits include recurring units derived from alkyl or aryl(meth)acrylates, hydroxyl or lactone-bearing (meth)acrylates, styrene,vinylnaphthalene, vinylanthracene, vinylpyrene, vinylcarbazole, indene,acenaphthylene, norbornenes, norbornadienes, tricyclodecenes, andtetracyclododecenes.

The preferred base polymers from which the reversal film is formed arehydrocarbon polymers, especially polymers comprising aromaticgroup-bearing hydrocarbons.

As the silicon-containing material for use in the reversal film-formingcomposition, silicon polymers based on silsesquioxane are preferred fromthe standpoint of etch resistance.

The base polymer should preferably have a weight average molecularweight (Mw) of 1,000 to 200,000, and more preferably 1,500 to 100,000,as measured by GPC versus polystyrene standards. Also it shouldpreferably have a dispersity (Mw/Mn) of 1.0 to 7.0, and more preferably1.02 to 5.0.

In addition to the base polymer described above, the reversalfilm-forming composition may comprise a scarcely alkali soluble materialfor pattern reversal, an alkali soluble surfactant for enhancing asurface alkali dissolution rate, an alkali soluble etching resistanceimprover, a basic quencher, an organic solvent and the like.

Examples of the scarcely alkali soluble material for pattern reversalinclude fullerenes having phenol group or malonic acid substitutedthereon and oligomeric phenol compounds. These materials have a highcarbon content and the function of improving etching resistance as well.Pattern reversal materials may be used alone or in a blend of two ormore.

Examples of suitable materials include the phenolic compounds describedin JP-A 2006-259249, JP-A 2006-259482, JP-A 2006-285095, and JP-A2006-293298, the bisnaphthol compounds described in JP-A 2007-199653,and fluorene compounds having a phenol group, including4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-dimethyl-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-diallyl-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-difluoro-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-diphenyl-4,4′-(9H-fluoren-9-ylidene)bisphenol,2,2′-dimethoxy-4,4′-(9H-fluoren-9-ylidene)bisphenol,tetrahydrospirobiindene compounds,2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,3,3,3′,3′-tetramethyl-2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,3,3,3′,3′,4,4′-hexamethyl-2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-5,5′-diol,5,5′-dimethyl-3,3,3′,3′-tetramethyl-2,3,2′,3′-tetrahydro-(1,1′)-spirobiindene-6,6′-diol,tritylphenol, etc. These materials may be used as the alkali solubleetching resistance improver.

The above material is preferably added in an amount of 0 to 200 parts,and more preferably 0 to 100 parts by weight per 100 parts by weight ofthe base polymer. When added, the amount of the material is at least 1phr, and more preferably at least 5 phr.

Enhancing the alkali solubility of only a surface layer of the patternreversal film is advantageous for smoothing dissolution of the patternreversal film building up over the positive resist pattern which hasbeen altered to be alkali soluble, and for enhancing the dimensionalcontrol of a trench pattern or hole pattern converted from the positivepattern. To enhance the surface alkali solubility, an alkali solublesurfactant, especially fluorochemical surfactant may be added. Thepreferred fluorochemical surfactants are those comprising either one orboth of recurring units (s-1) and (s-2) represented by the generalformula (3).

Herein, R⁸ and R¹¹ are each independently hydrogen or methyl. The lettern is equal to 1 or 2. In case of n=1, X₁ is a phenylene group, —O—,—C(═O)—O—R¹⁴—, or —C(═O)—NH—R¹⁴— wherein R¹⁴ is a single bond or astraight or branched C₁-C₄ alkylene group which may have an ester orether radical. In case of n=2, X₁ is a phenylene group with one hydrogenatom eliminated (represented by —C₆H₃—), or —C(═O)—O—R⁸¹═ or—C(═O)—NH—R⁸¹═ wherein R⁸¹ is a straight, branched or cyclic C₁-C₁₀alkylene group with one hydrogen atom eliminated, which may have anester or ether radical. R⁹ is a single bond or a straight, branched orcyclic C₁-C₁₂ alkylene group. R¹⁰ is hydrogen, fluorine, methyl,trifluoromethyl or difluoromethyl, or R¹⁰ and R⁹ may bond together toform a ring of 3 to 10 carbon atoms (exclusive of aromatic ring) withthe carbon atom to which they are attached, which ring may have anether, fluorinated alkylene or trifluoromethyl radical. X₂ is aphenylene group, —O—, —C(═O)—O—R¹³—, or —C(═O)—NH—R¹³— wherein R¹³ is asingle bond or a straight or branched C₁-C₄ alkylene group which mayhave an ester or ether radical. R¹² is fluorine or a straight, branchedor cyclic C₁-C₂₀ alkyl group which is substituted with at least onefluorine atom and which may have an ether, ester or sulfonamide radical.The letter m is an integer of 1 to 5 when X₂ is phenylene, and m is 1when X₂ is otherwise.

Examples of the monomers from which units (s-1) are derived areillustrated below.

Herein R⁸ is as defined above.

Examples of the monomers from which recurring units (s-2) in formula (3)are derived are illustrated below while many recurring units (s-2) areunits having a fluorinated alkyl group.

Herein R¹¹ is as defined above.

These recurring units (s-1) and (s-2) may be copolymerized with theabove-described alkali soluble recurring units having a phenol orcarboxyl group or substantially alkali insoluble recurring units (s-3).In these copolymers, the proportion of recurring units (s-1) and (s-2)is 0≦(s-1)≦1, 0≦(s-2)≦1, and 0<(s-1)+(s-2)≦1, preferably0.1<(s-1)+(s-2)≦1, and more preferably 0.2<(s-1)+(s-2)≦1.Understandably, in the case of (s-1)+(s-2)<1, the balance consists ofrecurring units (s-3) described above.

This alkali soluble surfactant should preferably have a weight averagemolecular weight (Mw) of 1,000 to 100,000 and more preferably 2,000 to50,000.

The alkali soluble surfactant is preferably added in an amount of 0 to50 parts, and more preferably 0 to 20 parts by weight per 100 parts byweight of the base polymer. Too much amounts of the surfactant may causeexcessive film slimming or detract from etching resistance. When added,at least 1 phr of the surfactant is preferred.

The basic quencher used herein may be any of the same basic compounds asdescribed in conjunction with the positive resist composition.Specifically, a basic compound may be added to the pattern reversal filmused in the pattern forming process of the invention for preventing aciddiffusion from the resist pattern as developed. Particularly when anacid labile group-substituted phenolic compound or carboxyl-containingcompound is used as the component of the pattern reversal film, therearises the problem that the alkali dissolution rate increases due todiffusion of acid from the resist pattern and deprotection reaction,leading to the reversal pattern of an increased size or substantiallyreduced thickness. This problem is effectively overcome by adding abasic compound. Understandably the basic compounds added to the resistcomposition and the pattern reversal film composition may be the same ordifferent.

The basic compound or basic quencher is preferably added in an amount of0 to 10 parts, and more preferably 0 to 5 parts by weight per 100 partsby weight of the base polymer. When added, at least 0.1 phr of thequencher is preferred.

To the reversal film-forming composition, an onium salt acid generatormay be added. When an onium salt is added to a reversal film-formingcomposition comprising a phenol base material as the base polymer, thecomposition has a reduced alkali dissolution rate due to thedissolution-inhibiting effect of the onium salt. The addition of anonium salt is effective for tailoring the alkali dissolution rate.

In the pattern reversal film-forming composition used in the patternforming process of the invention, the organic solvent used may beselected from those used in the positive resist composition, and fromalcohols of 3 to 10 carbon atoms and ethers of 8 to 12 carbon atomswhich are favorable in preventing mixing with the positive resistcoating (i.e., resist pattern). Illustrative examples of the C₃-C₁₀alcohols include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-diethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol.

Examples of the C₈-C₁₂ ethers include di-n-butyl ether, diisobutylether, di-sec-butyl ether, di-n-pentyl ether, diisopentyl ether,di-sec-pentyl ether, di-t-amyl ether, and di-n-hexyl ether. Thesesolvents may be used alone or in admixture of two or more. An aromaticsolvent such as toluene, xylene or anisole may be mixed with theforegoing solvent.

The amount of the organic solvent used is preferably 200 to 3,000 parts,and more preferably 400 to 2,000 parts by weight per 100 parts by weightof the base polymer.

Process

Now referring to the drawings, the pattern forming process of theinvention is illustrated. First, the positive resist composition iscoated on a substrate to form a resist film thereon. As shown in FIG.4A, a resist film 30 of a positive resist composition is formed on aprocessable substrate 20 disposed on a substrate 10 directly or via anintermediate intervening layer (not shown). The resist film preferablyhas a thickness of 10 to 1,000 nm and more preferably 20 to 500 nm.Prior to exposure, the resist film is heated or prebaked, preferably ata temperature of 60 to 180° C., especially 70 to 150° C. for a time of10 to 300 seconds, especially 15 to 200 seconds.

The substrate 10 used herein is generally a silicon substrate. Theprocessable substrate (or target film) 20 used herein includes SiO₂,SiN, SiON, SiOC, p-Si, α-Si, TiN, WSi, BPSG, SOG, Cr, CrO, CrON, MoSi,low dielectric film, and etch stopper film. The intermediate interveninglayer includes hard masks of SiO₂, SiN, SiON or p-Si, an undercoat inthe form of carbon film, a silicon-containing intermediate film, and anorganic antireflective coating.

Suitable spin-on carbon films include nortricyclene copolymers describedin JP-A 2004-205658, hydrogenated naphthol novolac resins described inJP-A 2004-205676, naphthol dicyclopentadiene copolymers described inJP-A 2004-205685, phenol dicyclopentadiene copolymers described in JP-A2004-354554 and JP-A 2005-010431, fluorene bisphenol novolac describedin JP-A 2005-128509, acenaphthylene copolymers described in JP-A2005-250434, indene copolymers described in JP-A 2006-053543, phenolgroup-containing fullerene described in JP-A 2006-227391, bisphenolcompounds and novolac resins thereof described in JP-A 2006-259249, JP-A2006-293298, and JP-A 2007-316282, bisphenol compounds and novolacresins thereof described in JP-A 2006-259482, novolac resins ofadamantane phenol compounds described in JP-A 2006-285095,hydroxyvinylnaphthalene copolymers described in JP-A 2007-171895,bisnaphthol compounds and novolac resins thereof described in JP-A2007-199653, ROMP polymers described in JP-A 2008-26600, andtricyclopentadiene copolymers described in JP-A 2008-96684, and otherresinous compounds.

The spin-on silicon-containing intermediate layers are preferably thoselayers comprising silsesquioxane-based silicon compounds and having anantireflection function as described in JP-A 2004-310019, JP-A2005-15779, JP-A 2005-18054, JP-A 2005-352104, JP-A 2007-65161, JP-A2007-163846, JP-A 2007-226170, and JP-A 2007-226204.

Where the reversal film is formed of a hydrocarbon base material, acarbon film having a carbon content of at least 75% by weight on theprocessable substrate and a silicon-containing intermediate layerthereon are preferably disposed between the processable substrate andthe photoresist film for positive/negative reversal to construct a filmstack suited for the three-layer resist process. The carbon film may beformed by spin coating or an amorphous carbon film formed by CVD. Thesilicon-containing intermediate layer may be a SOG film formed by spincoating or a film selected from SiO₂, SiN, SiON and TiN films formed byCVD or ALD, and has both functions of a hard mask for the carbon filmand an antireflection film.

Also, an organic antireflective coating may be formed between thesilicon-containing film and the photoresist film for the purposes ofpreventing footing on the substrate and pattern collapse and furtherreducing substrate reflection.

Where the reversal film is formed of a silicon-containing material, acarbon film having a carbon content of at least 75% by weight is formedbetween the processable substrate and the photoresist film forpositive/negative reversal, and a photoresist film is formed thereon. Anorganic antireflective coating may be formed between the carbon film andthe photoresist film. In this embodiment, the silicon-containingreversal film functions as a hard mask during processing of the carbonfilm.

This is followed by exposure. For the exposure, preference is given tohigh-energy radiation having a wavelength of 140 to 250 nm, andespecially ArF excimer laser radiation of 193 nm. The exposure may bedone either in air or in a dry atmosphere with a nitrogen stream, or byimmersion lithography in water. The ArF immersion lithography usesdeionized water or liquids having a refractive index of at least 1 andhighly transparent to the exposure wavelength such as alkanes as theimmersion solvent. The immersion lithography involves prebaking a resistfilm and exposing the resist film to light through a projection lens,with water introduced between the resist film and the projection lens.Since this allows lenses to be designed to a NA of 1.0 or higher,formation of finer feature size patterns is possible. The immersionlithography is important for the ArF lithography to survive to the 45-nmnode. In the case of immersion lithography, deionized water rinsing (orpost-soaking) may be carried out after exposure for removing waterdroplets left on the resist film, or a protective film may be appliedonto the resist film after pre-baking for preventing any leach-out fromthe resist film and improving water slip on the film surface.

The resist protective film used in the immersion lithography ispreferably formed from a solution of a polymer having1,1,1,3,3,3-hexafluoro-2-propanol residues which is insoluble in water,but soluble in an alkaline developer liquid, in a solvent selected fromalcohols of at least 4 carbon atoms, ethers of 8 to 12 carbon atoms, andmixtures thereof. The protective coating composition used herein maycomprise a base resin comprising predominant recurring units (P-1) suchas recurring units having 1,1,1,3,3,3-hexafluoro-2-propanol residues ora base resin comprising the predominant recurring units (P-1) andrecurring units (P-2) having a fluoroalkyl group copolymerizedtherewith. Examples of recurring units (P-1) include those derived fromthe monomers exemplified above for units (s-1), and examples ofrecurring units (P-2) include those derived from the monomersexemplified above for units (s-2). The proportion of these recurringunits (P-1) and (P-2) is 0<(P-1)≦1.0, 0≦(P-2)<1.0, and0.3≦(P-1)+(P-2)≦1.0. The base resin has a weight average molecularweight (Mw) of 1,000 to 100,000, and preferably 2,000 to 50,000. When abase resin free of recurring units (P-2) is used, it is preferred toincorporate an amine compound in the protective coating composition. Theamine compound used herein may be selected from those described above inconjunction with the basic compound. The amine compound is preferablyused in an amount of 0.01 to 10 parts, and more preferably 0.02 to 8parts by weight per 100 parts by weight of the base resin.

After formation of the photoresist film, deionized water rinsing (orpost-soaking) may be carried out for extracting the acid generator andthe like from the film surface or washing away particles, or afterexposure, rinsing (or post-soaking) may be carried out for removingwater droplets left on the resist film.

Exposure is preferably carried out so as to provide an exposure dose ofabout 1 to 200 mJ/cm², more preferably about 10 to 100 mJ/cm². This isfollowed by baking (PEB) on a hot plate at 60 to 150° C. for 1 to 5minutes, preferably at 80 to 120° C. for 1 to 3 minutes.

Thereafter the resist film is developed with a developer in the form ofan aqueous alkaline solution, for example, an aqueous solution of 0.1 to5 wt %, preferably 2 to 3 wt % TMAH for 0.1 to 3 minutes, preferably 0.5to 2 minutes by conventional techniques such as dip, puddle or spraytechniques. In this way, a desired resist pattern 30 a is formed on thesubstrate as shown in FIG. 4B.

As to the pattern, a dot pattern having a half-pitch size of 38×38 nm to100×100 nm, and especially 40×40 nm to 80×80 nm may be formed using alattice-like pattern mask. Since the size of a dot pattern depends onthe lens NA of an exposure tool, use of an NA 1.35 exposure tool enablesformation of dots having a half-pitch of 38 nm as the minimum size. Thedots may have longitudinal and transverse axes of equal or differentlength. The method of forming a dot pattern is not particularly limited.A typical method of forming a dot pattern is by exposing the resist filmto high-energy radiation through a lattice-like pattern phase shift maskand developing to form a dot pattern. With this method, holes having thefinest half-pitch can be formed.

In the prior art, an attempt to form a dot pattern having such a finepitch required two exposures through two masks by double dipolelithography. Specifically, the method includes a first exposure of Xdirection lines by dipole illumination, exchange of a mask, and a secondexposure of Y direction lines by dipole illumination. In this case,throughput drops due to mask exchange and alignment associatedtherewith. Also, any misalignment between the two exposures leads to apositional shift of finally formed holes. If the position of a holediffers from the position of a line to be connected thereto, this causesa failure of interconnection. Thus the double dipole illumination methodrequires a very high accuracy of alignment.

In contrast to the fact that the pattern formed by two exposures bydouble dipole illumination suffers from misalignment of the secondexposure, the pattern forming process of the invention is devoid ofmisalignment because only a single exposure is necessary. Because of nomask exchange and the only one exposure, there is an advantage of highthroughput.

Next, PEB and development are carried out to form a dot pattern. Arandom pitch dot pattern may be formed through a single development (seeFIG. 4B).

Next, the resist pattern is treated to eliminate acid labile groups inthe polymer (base resin) in the pattern and to crosslink the polymer,forming a crosslinked pattern 30 b (FIG. 4C). To induce elimination ofacid labile groups and crosslinking on the polymer in the resistpattern, acid and heat are necessary. In practice, once an acid isgenerated, heat is applied to effect elimination or deprotection of acidlabile groups and crosslinking at the same time. The acid may begenerated by a suitable method such as flood exposure of the wafer(pattern) as developed for decomposing the photoacid generator. Theflood exposure uses an illumination wavelength of 180 to 400 nm and anexposure dose of 10 mJ/cm² to 1 J/cm². Radiation with a wavelength ofless than 180 nm, specifically irradiation of excimer lasers or excimerlamps of 172 nm, 146 nm and 122 nm is undesirable because not only thegeneration of acid from photoacid generator, but also photo-inducedcrosslinking reaction are accelerated, leading to a decrease of alkalinedissolution rate due to exaggerated crosslinking. For the floodexposure, use is preferably made of an ArF excimer laser with awavelength of 193 nm or more, a KrCl excimer lamp of 222 nm, a KrFexcimer laser of 248 nm, a low-pressure mercury lamp centering at 254nm, a XeCl excimer lamp of 308 nm, and i-line of 365 nm. In analternative embodiment wherein a thermal acid generator in the form ofan ammonium salt is added to the positive resist composition, the acidcan be generated by heating. In this embodiment, acid generation andcrosslinking reaction take place simultaneously. Preferred heatingconditions include a temperature of 150 to 400° C., especially 160 to300° C. and a time of 10 to 300 seconds. As a result, a crosslinkedresist pattern which is insoluble in the solvent of the reversalfilm-forming composition is yielded. Since an additional illuminationsystem is necessary to generate the acid by illumination, the latterembodiment is more advantageous that uses a resist composition having athermal acid generator added thereto so that deprotection andcrosslinking reaction may be driven only by heating.

Next, as shown in FIG. 4D, the reversal film-forming composition isbuilt up until it covers the crosslinked resist pattern 30 b, forming areversal film 40. Preferably the thickness of the reversal film 40 isequal to the height of the resist pattern 30 b or ±30 nm.

Next, the liquid alkaline developer is applied to dissolve a surfacelayer of the reversal film 40 until the crosslinked resist pattern 30 bis exposed. From this point of time downward, the crosslinked resistpattern 30 b is selectively dissolved since the dissolution rate in thealkaline developer of the crosslinked resist pattern 30 b issubstantially higher than that of the reversal film 40. Eventually, thecrosslinked resist pattern 30 b is dissolved away, yielding the reversalfilm 40 provided with a reversal pattern 40 a which is a negative of thecrosslinked resist pattern 30 b as shown in FIG. 4E. If the resistpattern is a dot pattern, the resulting reversal pattern is a holepattern.

The hole pattern printed as the reversal pattern may be shrunk bybaking. That is, the size of holes may be reduced by baking. The bakingis preferably at a temperature of 70 to 180° C., preferably 80 to 170°C. for a time of 10 to 300 seconds.

In another embodiment, the hole pattern printed as the reversal patternmay be shrunk by the RELACS method. Specifically, a shrinking agent iscoated on the hole pattern and the structure is baked for shrinking thehole pattern. Useful materials are described in JP 3071401, JP-A2001-228616, JP-A 2004-86203, JP-A 2004-294992, JP-A 2007-206728, and WO2005/008340.

Typically a composition comprising a base polymer and theabove-mentioned crosslinker in water or alcohol may be used as theshrinking agent. The base polymer is selected from among polyacrylicacid, polyvinyl alcohol, polyvinyl acetal, polyvinyl pyrrolidone,polyethylene imine, polyethylene oxide, polyvinylamine, polyallylamine,styrene-maleic acid copolymers, poly(N-vinylformamide), polyoxazoline,melamine resins, urea resins, alkyd resins, and water-soluble resinsbased on sulfonamide or carbonamide.

A shrinking agent is coated on the hole pattern and baked so that theshrinking agent is attached to the reversed film. The baking ispreferably at a temperature of 70 to 180° C., preferably 80 to 150° C.for a time of 10 to 300 seconds. Then the extra shrinking agent may beremoved using water, alcohol, alkaline developer or a mixture thereof.

When a phenol base material is used as the reversal film in the patternforming process, advantageously the pattern is amenable to shrinkage bythe thermal flow and RELACS methods. A positive resist compositioncomprising a phenol base material forms a film having a glass transitiontemperature (Tg) which varies between dense and isolated hole patternsdue to the difference in partial elimination amount of acid labilegroups therebetween. The dense hole pattern is largely affected by foglight so that more partial deprotection takes place than in the isolatedhole pattern, leading to a higher Tg. This reduces the quantity ofdeformation by flow and hence the shrinkage of holes. The reversal filmmaterial used in the pattern forming process is free of a difference inTg of film between dense and isolated hole patterns because it does notresort to pattern formation by light exposure. This provides theadvantage that there is no difference in shrinkage between dense andisolated holes.

Furthermore, as shown in FIG. 4F, using the reversal pattern 40 a as amask, the intermediate intervening layer of hard mask or the like (ifany) is etched, and the processable substrate 20 further etched. Foretching of the intermediate intervening layer of hard mask or the like,dry etching with fluorocarbon or halogen gases may be used. For etchingof the processable substrate, the etching gas and conditions may beproperly chosen so as to establish an etching selectivity relative tothe hard mask, and specifically, dry etching with fluorocarbon, halogen,oxygen, hydrogen or similar gases may be used. Thereafter, second resistfilm is removed. Removal of the film may be carried out after etching ofthe intermediate intervening layer of hard mask or the like. It is notedthat removal of the second resist film may be achieved by dry etchingwith oxygen or radicals and removal of the second resist film may beachieved as previously described, or using strippers such as amines,sulfuric acid/aqueous hydrogen peroxide or organic solvents.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation. The abbreviation “pbw” is parts by weight. For allpolymers, Mw and Mn are determined by GPC versus polystyrene standards.

Synthesis Examples

A polymer for use in a reversal film-forming composition was prepared bycombining monomers, effecting copolymerization reaction intetrahydrofuran medium, crystallization in methanol, repeatedly washingwith hexane, isolation, and drying. The resulting polymer (Polymer 1)had the composition shown below. Notably, a phenol group on a monomerwas substituted by an acetoxy group, which was converted back to aphenol group by alkaline hydrolysis after polymerization. Thecomposition of the polymer was analyzed by ¹H-NMR, and the Mw and Mw/Mndetermined by GPC.

Polymer 1

-   -   Mw=9,300    -   Mw/Mn=1.88

A reversal film-forming composition was prepared by combining Polymer 1,a basic compound, and a solvent in accordance with the formulation ofTable 1. To the solvent, 100 ppm of a fluorochemical surfactant FC-4430(3M-Sumitomo Co., Ltd.) was added. The reversal film-forming compositionwas coated onto a HMDS-primed 8-inch silicon substrate and baked at 110°C. for 60 seconds to form a pattern reversal film (IROC-1) of 60 nmthick. The film was developed with a developer in the form of a 2.38 wt% TMAH aqueous solution for 30 seconds. A film thickness reduction bydevelopment was determined, from which a dissolution rate (in nm/s) wascomputed. The result is shown in Table 1.

-   Basic compound: Basic quencher 1 of the following structural formula

-   Organic solvent: PGMEA (propylene glycol monomethyl ether acetate)

TABLE 1 Pattern reversal film-forming composition Dissolution ReversalPolymer Additive Solvent rate film (pbw) (pbw) (pbw) (nm/s) IROC-1Polymer 1 Basic PGMEA 0.2 (100) quencher 1 (3,000) (2.0)Preparation of Positive Resist Composition and Alkali-Soluble ProtectiveCoating Composition

A resist solution and a protective coating solution were prepared bydissolving polymers (Resist polymer and Protective film polymer) andcomponents in solvents in accordance with the formulation of Tables 2and 3, and filtering through a filter with a pore size of 0.2 μm. Thecomponents in Tables 2 and 3 are identified below.

-   Photoacid generator: PAG1 of the following structural formula

Resist Polymer 1

-   -   Mw=8,310    -   Mw/Mn=1.73

Protective Film Polymer

-   -   Mw=8,800    -   Mw/Mn=1.69

-   Basic compound: Basic quencher 2 of the following structural formula

Thermal Acid Generator:

-   -   TAG1 of the following structural formula

-   Organic solvent: PGMEA (propylene glycol monomethyl ether acetate)

TABLE 2 Acid Basic Organic Polymer generator compound solvent (pbw)(pbw) (pbw) (pbw) Resist 1 Resist PAG1 (12.0) Basic PGMEA Polymer 1 TAG1(0.5) quencher 2 (2,000) (100) (1.20)

TABLE 3 Polymer Additive Organic solvent (pbw) (pbw) (pbw) TC-1Protective tri-n-octylamine diisoamyl ether (2,700) Film Polymer (0.3)2-methyl-1-butanol (270) (100)Film Thickness Change in Solvent and Alkali Dissolution Rate afterHigh-Temperature Baking

On a substrate (silicon wafer), the resist composition prepared inaccordance with the formulation of Table 2 was spin coated and baked ona hot plate at 190° C. for 60 seconds to form a resist film of 150 nmthick.

A solvent was statically dispensed on the resist film for 30 seconds.Thereafter, the sample was rotated at 2000 rpm for 30 seconds forspinning off the solvent and baked at 100° C. for 60 seconds for dryingoff the solvent. A film thickness was measured using a film thicknessgauge, and a change of film thickness from the film as baked at 190° C.was computed.

Separately, the resist film as baked at 190° C. was examined foralkaline dissolution rate. Using a resist development analyzer RDA-790(Lithotec Japan Co., Ltd.), an alkaline dissolution rate of the film in2.38 wt % TMAH aqueous solution was measured. The results are shown inTable 4.

TABLE 4 Film slimming by solvent Alkali dissolution rate Solvent (nm)(nm/s) Resist 1 PGMEA 0.5 170

Examples 1, 2 and Comparative Examples 1, 2 ArF Lithography Patterning

On a substrate (silicon wafer), a spin-on carbon film ODL-50 (Shin-EtsuChemical Co., Ltd.) having a carbon content of 80 wt % was deposited toa thickness of 200 nm and a silicon-containing spin-on hard maskSHB-A941 having a silicon content of 43 wt % was deposited thereon to athickness of 35 nm. On this substrate for trilayer process, the resistcomposition shown in Table 2 was spin coated, then baked on a hot plateat 100° C. for 60 seconds to form a resist film of 100 nm thick. Theprotective coating composition TC-1 shown in Table 3 was spin coated onthe resist film and baked at 90° C. for 60 seconds to form a protectivefilm of 50 nm thick.

In Example 1, using an ArF excimer laser immersion lithography scannerNSR-610C (Nikon Corp., NA 1.30, 0.98/0.78, cross pole opening 20 deg.,azimuthally polarized illumination), exposure was performed through a 6%halftone phase shift mask having the layout and dimensions shown in FIG.34. After the exposure, the sample was baked (PEB) at 100° C. for 60seconds and developed with a 2.38 wt % TMAH aqueous solution for 30seconds.

Example 2 used the same film construction and mask as in Example 1.Using an ArF excimer laser immersion lithography scanner NSR-610C (NikonCorp., NA 1.30, a 0.98/0.78, dipole opening 20 deg., azimuthallypolarized illumination), two exposures of X-direction dipoleillumination and Y-direction dipole illumination were successivelyperformed. After the exposure, the sample was baked (PEB) at 100° C. for60 seconds and developed with a 2.38 wt % TMAH aqueous solution for 30seconds.

Comparative Example 1 used the same film construction and exposure toolas in Example 1. Exposure was performed through the mask of FIG. 35under conditions: NA 1.30, a 0.98/0.78, cross-pole opening 20 deg., andazimuthally polarized illumination. After the exposure, the sample wassimilarly processed.

By observation under TDSEM S-9380 (Hitachi Hitechnologies Ltd.), thesize of dots as developed, dots as heated, and holes as image reversedwas measured. The dots observed correspond to locations A-1, B-1, C-1and D-1 on the mask of FIG. 34 in Examples 1 and 2, and locations A-2,B-2, C-2 and D-2 on the mask of FIG. 35 in Comparative Example 1. Theresults are shown in Table 5.

Comparative Example 2 used the same film construction and exposure toolas in Example 1. Hole pattern exposure was performed through alattice-like mask with the layout of FIG. 15 having a pitch of 90 nm anda line width of 25 mm (or a hole size of 65 nm). After the exposure, thesample was baked (PEB) at 100° C. for 60 seconds and developed with a2.38 wt % TMAH aqueous solution for 30 seconds. By observation underTDSEM S-9380 (Hitachi Hitechnologies Ltd.), the size of holes wasmeasured. The minimum size of holes resolved was 50 nm while holes ofsmaller size could not be resolved.

TABLE 5 Results of reversal from dot pattern to hole pattern (size innm) After development After baking After reversal A-1 B-1 C-1 D-1 A-1B-1 C-1 D-1 A-1 B-1 C-1 D-1 Example 1 32 31 30 30 31 31 30 29 32 33 3232 Example 2 33 33 33 32 34 34 33 30 35 35 36 34 After development Afterbaking After reversal A-2 B-2 C-2 D-2 A-2 B-2 C-2 D-2 A-2 B-2 C-2 D-2Comparative 30 25 15 12 31 24 12 10 not reversed Example 1

It is evident from Table 5 that in the pattern forming process ofExample 1, 30-nm hole patterns including 1:1 dense holes at a pitch of90 nm and isolated holes were opened through a single exposure. InExample 2, 30-nm hole patterns including 1:1 dense holes at a pitch of90 nm and isolated holes were opened through two double dipoleillumination exposures. By contrast, the prior art process ofComparative Example 1 failed to open hole patterns after reversaloperation, because a substantial size difference arose between dense andisolated patterns and the dot pattern after development experienced afilm slimming. In the attempt to resolve holes at a pitch of 90 nmthrough exposure and development in accordance with the prior artprocess, the smallest holes had a size of 50 nm.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention.Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

Japanese Patent Application No. 2009-030281 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A process for forming a pattern by way of positive/negative reversal,comprising the steps of: coating a chemically amplified positive resistcomposition onto a processable substrate, the resist compositioncomprising a resin comprising recurring units of structure having acidlabile groups which are eliminatable with acid, the resin turning to besoluble in an alkaline developer as a result of elimination of the acidlabile groups, a photoacid generator capable of generating an acid uponexposure to high-energy radiation and optionally, a thermal acidgenerator capable of generating an acid upon heating, and an organicsolvent, prebaking the coating to remove the solvent and to form aresist film, exposing the resist film to high-energy radiation through aphase shift mask including a lattice-like first shifter having a linewidth equal to or less than half a pitch and a second shifter arrayed onthe first shifter and consisting of lines whose on-wafer size is 2 to 30nm thicker than the line width of the first shifter, post-exposurebaking so that the acid generated by the acid generator upon exposureacts on acid labile groups in the resin for thereby effectingelimination reaction of acid labile groups in the resin in exposedareas, developing the exposed resist film with an alkaline developer toform a positive pattern, illuminating or heating the positive pattern,the acid generated by illumination or the heat serving to eliminate acidlabile groups in the resin in the positive pattern for therebyincreasing the alkaline solubility of the resin and to induce crosslinksin the resin to such an extent that the resin does not lose solubilityin an alkaline wet etchant, for thereby endowing the positive patternwith resistance to an organic solvent used in a reversal film-formingcomposition, coating a reversal film-forming composition on the positivepattern-bearing substrate to form a reversal film, and dissolving awaythe crosslinked positive pattern using an alkaline wet etchant.
 2. Theprocess of claim 1 wherein the second shifter is arrayed on the firstshifter.
 3. The process of claim 1 wherein the second shifter is ofcrisscross or lattice-like shape.
 4. The process of claim 1 wherein thestep of developing the exposed resist film is to form a pattern of dotsonly at the intersections between gratings of the second shifter.
 5. Theprocess of claim 1 wherein the lattice-like first shifter is a halftonephase shift mask having a transmittance of 3 to 15%.
 6. The process ofclaim 1 wherein the phase shift mask includes the first shifter having aline width equal to or less than ⅓ of the pitch and the second shifterconsisting of lines whose on-wafer size is 2 to 30 nm thicker than theline width of the first shifter.
 7. The process of claim 1 wherein inthe step of illuminating or heating the positive pattern for increasingthe alkaline solubility of the resin and for endowing the positivepattern with resistance to an organic solvent used in a reversalfilm-forming composition, the dissolution rate of the crosslinkedpositive pattern in an alkaline wet etchant is such that the crosslinkedpositive pattern exhibits an etching rate in excess of 2 nm/sec whenetched with 2.38 wt % TMAH aqueous solution, the organic solvent used inthe reversal film-forming composition is selected from the groupconsisting of propylene glycol monomethyl ether acetate, cyclohexanone,ethyl lactate, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, propylene glycol monopropyl ether, propylene glycolmonobutyl ether, and heptanone, and mixtures of two or more of theforegoing, the resistance to organic solvent of the crosslinked positivepattern is such that the crosslinked positive pattern experiences a filmslimming of up to 10 nm when contacted with the organic solvent for 30seconds.
 8. The process of claim 1 wherein said reversal film-formingcomposition comprises a resin comprising monomeric units of aromatic oralicyclic structure.
 9. The process of claim 1, further comprising,between the step of coating a reversal film-forming composition on thepositive pattern-bearing substrate to form a reversal film and the stepof dissolving away the crosslinked positive pattern using an alkalinewet etchant, the step of removing the reversal film deposited on thecrosslinked positive pattern.
 10. The process of claim 9 wherein thestep of removing the reversal film deposited on the crosslinked positivepattern includes wet etching.
 11. The process of claim 10 wherein thereversal film is soluble in an alkaline wet etchant, but has adissolution rate which is slower than that of the crosslinked positivepattern after the step of endowing the positive pattern with resistanceto organic solvent, the wet etching uses an alkaline wet etchant, andthe step of removing the reversal film deposited on the crosslinkedpositive pattern and the step of dissolving away the crosslinkedpositive pattern are concurrently carried out.
 12. The process of claim11 wherein the reversal film has a dissolution rate of 0.02 nm/sec to 2nm/sec when etched with 2.38 wt % TMAH aqueous solution.
 13. The processof claim 1 wherein said chemically amplified positive resist compositioncomprises a component capable of generating an acid in the step ofheating for endowing the positive pattern with organic solventresistance.
 14. The process of claim 13 wherein the component capable ofgenerating an acid is a thermal acid generator which is added to theresist composition in addition to the photoacid generator.
 15. Theprocess of claim 14 wherein the thermal acid generator has the generalformula (P1a-2):

wherein R^(101d), R^(101e), R^(101f), and R^(101g) are eachindependently hydrogen, a straight, branched or cyclic C₁-C₁₂ alkyl,alkenyl, oxoalkyl or oxoalkenyl group, a C₆-C₂₀ aryl group, or a C₇-C₁₂aralkyl or aryloxoalkyl group, in which some or all hydrogen atoms maybe substituted by alkoxy groups, or R^(101d) and R^(101e), or R^(101d),R^(101e) and R^(101f) may bond together to form a ring with the nitrogenatom to which they are attached, each of R^(101e) and R^(101f) or eachof R^(101d), and R^(101e) and R^(101f) is a C₃-C₁₀ alkylene group or ahetero-aromatic ring having incorporated therein the nitrogen atom whenthey form a ring, and K⁻ is a sulfonate having at least one α-positionfluorinated, perfluoroalkylimidate or perfluoroalkylmethidate.
 16. Theprocess of claim 1 wherein in said chemically amplified positive resistcomposition, the resin comprises recurring units having a lactone ringand recurring units having an acid labile group which is eliminatablewith acid.
 17. The process of claim 1 wherein in said chemicallyamplified positive resist composition, the resin comprises anelectrophilic partial structure which is an ester group or cyclic etherwhich will form crosslinks in the resin of the positive resist pattern.18. The process of claim 17 wherein in said chemically amplifiedpositive resist composition, the resin comprises recurring units havinga 7-oxanorbornane ring and recurring units having an acid labile groupwhich is eliminatable with acid, and heat is applied in the step ofilluminating the positive pattern to generate an acid wherebyelimination of acid labile groups and crosslinking of the resin takeplace simultaneously in the positive pattern.
 19. The process of claim18 wherein the recurring units having a 7-oxanorbornane ring arerecurring units (a) having the general formula (1):

wherein R¹ is hydrogen or methyl, R² is a single bond or a straight,branched or cyclic C₁-C₆ alkylene group which may have an ether or esterradical, and which has a primary or secondary carbon atom through whichit is linked to the ester group in the formula, R³, R⁴, and R⁵ are eachindependently hydrogen or a straight, branched or cyclic C₁-C₆ alkylgroup, and “a” is a number in the range: 0<a<1.0.
 20. The process ofclaim 16 wherein the recurring units having an acid labile group whichis eliminatable with acid are recurring units (b) having the generalformula (2):

wherein R⁶ is hydrogen or methyl, R⁷ is an acid labile group, and b is anumber in the range: 0<b≦0.8.
 21. The process of claim 20 wherein theacid labile group of R⁷ is an acid labile group of alicyclic structurewhich is eliminatable with acid.
 22. The process of claim 1 wherein thepositive pattern comprises a dot pattern, and the pattern resulting frompositive/negative reversal comprises a hole pattern.
 23. The process ofclaim 1 wherein the positive pattern comprises both a dense dot patternand an isolated dot pattern, and the pattern resulting frompositive/negative reversal comprises both a dense hole pattern and anisolated hole pattern.
 24. The process of claim 23 wherein a dense dotpattern and an isolated dot pattern are formed as the positive patternby exposure to a dense dot pattern and subsequent exposure to anunnecessary portion of the dot pattern, and a dense hole pattern and anisolated hole pattern are formed by positive/negative reversaltherefrom.
 25. A process for forming a pattern by way ofpositive/negative reversal, comprising the steps of: coating achemically amplified positive resist composition onto a processablesubstrate, said resist composition comprising a resin comprisingrecurring units having acid labile groups which are eliminatable withacid, a photoacid generator capable of generating an acid upon exposureto high-energy radiation and a solvent, heating to remove the solvent toform a resist film, coating a protective film-forming composition ontothe resist film and drying to form a protective film, exposing theresist film to high-energy radiation in a repeating dense pattern from aprojection lens, by immersion lithography with water or a transparentliquid having a refractive index of at least 1 intervening between theresist film and the projection lens, further exposing a region of thedense pattern or unexposed area by immersion lithography, post-exposurebaking for causing the acid generated by the acid generator uponexposure to act on the acid labile groups on the resin whereby the acidlabile groups on the resin in the exposed area undergo eliminationreaction, and developing the exposed resist film with an alkalinedeveloper to form a positive pattern, treating the positive pattern soas to eliminate the acid labile groups on the resin in the positivepattern resulting from the previous step, and to induce crosslinking inthe resin to such an extent that the resin does not lose solubility inan alkaline wet etchant, for thereby endowing the positive pattern withresistance to an organic solvent to be used in a reversal film-formingcomposition, coating a reversal film-forming composition thereon to forma reversal film, and dissolving away the positive pattern using analkaline wet etchant.
 26. The process of claim 25 wherein saidprotective film-forming composition is based on a copolymer comprisingamino-containing recurring units.
 27. The process of claim 25 whereinsaid protective film-forming composition further comprises an aminecompound.
 28. The process of claim 1, further comprising the steps offorming a carbon film having a carbon content of at least 75% by weighton the processable substrate, forming a silicon-containing intermediatefilm thereon, and coating a resist composition for positive/negativereversal thereon, the reversal film being formed of a hydrocarbon-basedmaterial.
 29. The process of claim 1, further comprising the steps offorming a carbon film having a carbon content of at least 75% by weighton the processable substrate, and coating a resist composition forpositive/negative reversal thereon, the reversal film being formed of asilicon-containing material.
 30. The process of claim 1, furthercomprising the steps of forming a carbon film having a carbon content ofat least 75% by weight on the processable substrate, forming an organicantireflection film thereon, and coating a resist composition forpositive/negative reversal thereon, the reversal film being formed of asilicon-containing material.